Code cleanup around MOTOR_CURRENT_PWM options

Marlin/Conditionals.h

   #define HAS_E3_STEP (PIN_EXISTS(E3_STEP))
   #define HAS_E4_STEP (PIN_EXISTS(E4_STEP))
 
+  #define HAS_MOTOR_CURRENT_PWM (PIN_EXISTS(MOTOR_CURRENT_PWM_XY) || PIN_EXISTS(MOTOR_CURRENT_PWM_Z) || PIN_EXISTS(MOTOR_CURRENT_PWM_E))
+
   /**
    * Helper Macros for heaters and extruder fan
    */

Marlin/Marlin_main.cpp

     if (code_seen('B')) digipot_current(4, code_value());
     if (code_seen('S')) for (int i = 0; i <= 4; i++) digipot_current(i, code_value());
   #endif
-  #ifdef MOTOR_CURRENT_PWM_XY_PIN
+  #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
     if (code_seen('X')) digipot_current(0, code_value());
   #endif
-  #ifdef MOTOR_CURRENT_PWM_Z_PIN
+  #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
     if (code_seen('Z')) digipot_current(1, code_value());
   #endif
-  #ifdef MOTOR_CURRENT_PWM_E_PIN
+  #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
     if (code_seen('E')) digipot_current(2, code_value());
   #endif
   #if ENABLED(DIGIPOT_I2C)

Marlin/servo.h

   //#define _useTimer1
   #define _useTimer3
   #define _useTimer4
-  #ifndef MOTOR_CURRENT_PWM_XY_PIN
-    //Timer 5 is used for motor current PWM and can't be used for servos.
-    #define _useTimer5
-    //typedef enum { _timer5, _timer1, _timer3, _timer4, _Nbr_16timers } timer16_Sequence_t ;
-    typedef enum { _timer5, _timer3, _timer4, _Nbr_16timers } timer16_Sequence_t ;
-  #else
-    typedef enum {_timer3, _timer4, _Nbr_16timers } timer16_Sequence_t ;
+  #if !HAS_MOTOR_CURRENT_PWM
+    #define _useTimer5 // Timer 5 is used for motor current PWM and can't be used for servos.
   #endif
-
 #elif defined(__AVR_ATmega32U4__)
-  //#define _useTimer1
   #define _useTimer3
-  //typedef enum { _timer1, _Nbr_16timers } timer16_Sequence_t ;
-  typedef enum { _timer3, _Nbr_16timers } timer16_Sequence_t ;
-
 #elif defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB1286__)
   #define _useTimer3
-  //#define _useTimer1
-  //typedef enum { _timer3, _timer1, _Nbr_16timers } timer16_Sequence_t ;
-  typedef enum { _timer3, _Nbr_16timers } timer16_Sequence_t ;
-
-#elif defined(__AVR_ATmega128__) ||defined(__AVR_ATmega1281__) || defined(__AVR_ATmega1284P__) ||defined(__AVR_ATmega2561__)
+#elif defined(__AVR_ATmega128__) || defined(__AVR_ATmega1281__) || defined(__AVR_ATmega1284P__) || defined(__AVR_ATmega2561__)
   #define _useTimer3
-  //#define _useTimer1
-  //typedef enum { _timer3, _timer1, _Nbr_16timers } timer16_Sequence_t ;
-  typedef enum { _timer3, _Nbr_16timers } timer16_Sequence_t ;
+#else
+  // everything else
+#endif
 
-#else  // everything else
-  //#define _useTimer1
-  //typedef enum { _timer1, _Nbr_16timers } timer16_Sequence_t ;
-  typedef enum { _Nbr_16timers } timer16_Sequence_t ;
+typedef enum {
+  #if ENABLED(_useTimer1)
+    _timer1,
+  #endif
+  #if ENABLED(_useTimer3)
+    _timer3,
+  #endif
+  #if ENABLED(_useTimer4)
+    _timer4,
+  #endif
+  #if ENABLED(_useTimer5)
+    _timer5,
+  #endif
+  _Nbr_16timers
+} timer16_Sequence_t;
 
-#endif
 
 #define Servo_VERSION           2     // software version of this library
 

Marlin/stepper.cpp

   bool abort_on_endstop_hit = false;
 #endif
 
-#if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
+#if HAS_MOTOR_CURRENT_PWM
   #ifndef PWM_MOTOR_CURRENT
     #define PWM_MOTOR_CURRENT DEFAULT_PWM_MOTOR_CURRENT
   #endif
       digipot_current(i, digipot_motor_current[i]);
     }
   #endif
-  #ifdef MOTOR_CURRENT_PWM_XY_PIN
-    pinMode(MOTOR_CURRENT_PWM_XY_PIN, OUTPUT);
-    pinMode(MOTOR_CURRENT_PWM_Z_PIN, OUTPUT);
-    pinMode(MOTOR_CURRENT_PWM_E_PIN, OUTPUT);
-    digipot_current(0, motor_current_setting[0]);
-    digipot_current(1, motor_current_setting[1]);
-    digipot_current(2, motor_current_setting[2]);
+  #if HAS_MOTOR_CURRENT_PWM
+    #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
+      pinMode(MOTOR_CURRENT_PWM_XY_PIN, OUTPUT);
+      digipot_current(0, motor_current_setting[0]);
+    #endif
+    #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
+      pinMode(MOTOR_CURRENT_PWM_Z_PIN, OUTPUT);
+      digipot_current(1, motor_current_setting[1]);
+    #endif
+    #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
+      pinMode(MOTOR_CURRENT_PWM_E_PIN, OUTPUT);
+      digipot_current(2, motor_current_setting[2]);
+    #endif
     //Set timer5 to 31khz so the PWM of the motor power is as constant as possible. (removes a buzzing noise)
     TCCR5B = (TCCR5B & ~(_BV(CS50) | _BV(CS51) | _BV(CS52))) | _BV(CS50);
   #endif
   #if HAS_DIGIPOTSS
     const uint8_t digipot_ch[] = DIGIPOT_CHANNELS;
     digitalPotWrite(digipot_ch[driver], current);
-  #elif defined(MOTOR_CURRENT_PWM_XY_PIN)
+  #elif HAS_MOTOR_CURRENT_PWM
+    #define _WRITE_CURRENT_PWM(P) analogWrite(P, 255L * current / (MOTOR_CURRENT_PWM_RANGE))
     switch (driver) {
-      case 0: analogWrite(MOTOR_CURRENT_PWM_XY_PIN, 255L * current / (MOTOR_CURRENT_PWM_RANGE)); break;
-      case 1: analogWrite(MOTOR_CURRENT_PWM_Z_PIN, 255L * current / (MOTOR_CURRENT_PWM_RANGE)); break;
-      case 2: analogWrite(MOTOR_CURRENT_PWM_E_PIN, 255L * current / (MOTOR_CURRENT_PWM_RANGE)); break;
+      #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
+        case 0: _WRITE_CURRENT_PWM(MOTOR_CURRENT_PWM_XY_PIN); break;
+      #endif
+      #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
+        case 1: _WRITE_CURRENT_PWM(MOTOR_CURRENT_PWM_Z_PIN); break;
+      #endif
+      #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
+        case 2: _WRITE_CURRENT_PWM(MOTOR_CURRENT_PWM_E_PIN); break;
+      #endif
     }
   #else
     UNUSED(driver);