Add 'BTN_ENC_EN' for SKR V1.4 with DOGM (#19796)

Marlin/src/lcd/marlinui.cpp

       SET_INPUT_PULLUP(BTN_ENC);
     #endif
 
+    #if BUTTON_EXISTS(ENC_EN)
+      SET_INPUT_PULLUP(BTN_ENC_EN);
+    #endif
+
     #if BUTTON_EXISTS(BACK)
       SET_INPUT_PULLUP(BTN_BACK);
     #endif
 
           #endif // ENCODER_RATE_MULTIPLIER
 
-          encoderPosition += (encoderDiff * encoderMultiplier) / epps;
+          // Update position only when ENC_EN is HIGH
+          if (TERN1(BTN_ENC_EN, !BUTTON_PRESSED(ENC_EN)))
+            encoderPosition += (encoderDiff * encoderMultiplier) / epps;
+
           encoderDiff = 0;
         }
 
             if (BUTTON_PRESSED(EN2)) newbutton |= EN_B;
           #endif
           #if BUTTON_EXISTS(ENC)
-            if (BUTTON_PRESSED(ENC)) newbutton |= EN_C;
+            // Update button only when ENC_EN is HIGH
+            if (TERN1(BTN_ENC_EN, !BUTTON_PRESSED(ENC_EN)) && BUTTON_PRESSED(ENC)) newbutton |= EN_C;
           #endif
           #if BUTTON_EXISTS(BACK)
             if (BUTTON_PRESSED(BACK)) newbutton |= EN_D;

Marlin/src/pins/lpc1768/pins_BTT_SKR_V1_4.h

         #define LCD_PINS_D5                P1_21
         #define LCD_PINS_D6                P1_22
         #define LCD_PINS_D7                P1_23
+
+        #if ENABLED(REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER)
+          #define BTN_ENC_EN         LCD_PINS_D7  // Detect the presence of the encoder
+        #endif
+
       #endif
 
     #endif // !FYSETC_MINI_12864

Marlin/src/pins/pinsDebug_list.h

 #if defined(BTN_EN2) && BTN_EN2 >= 0
   REPORT_NAME_DIGITAL(__LINE__, BTN_EN2)
 #endif
+#if defined(BTN_ENC_EN) && BTN_ENC_EN >= 0
+  REPORT_NAME_DIGITAL(__LINE__, BTN_ENC_EN)
+#endif
 #if defined(BTN_ENC) && BTN_ENC >= 0
   REPORT_NAME_DIGITAL(__LINE__, BTN_ENC)
 #endif