Fix STM32 + SoftwareSerial compile (#17831)

Marlin/src/HAL/STM32/HAL.cpp

 #include "../../inc/MarlinConfig.h"
 #include "../shared/Delay.h"
 
-#if HAS_TMC_SW_SERIAL
-  #include "SoftwareSerial.h"
-#endif
-
 #if ENABLED(SRAM_EEPROM_EMULATION)
   #if STM32F7xx
     #include <stm32f7xx_ll_pwr.h>
     while (!LL_PWR_IsActiveFlag_BRR());   // Wait until backup regulator is initialized
   #endif
 
-  #if HAS_TMC_SW_SERIAL
-    SoftwareSerial::setInterruptPriority(SWSERIAL_TIMER_IRQ_PRIO, 0);
-  #endif
-
-  TERN_(HAS_TMC_SW_SERIAL, SoftwareSerial::setInterruptPriority(SWSERIAL_TIMER_IRQ_PRIO, 0));
+  SetSoftwareSerialTimerInterruptPriority();
 }
 
 void HAL_clear_reset_source() { __HAL_RCC_CLEAR_RESET_FLAGS(); }

Marlin/src/HAL/STM32/timers.cpp

 
 #define NUM_HARDWARE_TIMERS 2
 
-#ifndef SWSERIAL_TIMER_IRQ_PRIO
-  #define SWSERIAL_TIMER_IRQ_PRIO 1
-#endif
 #ifndef STEP_TIMER_IRQ_PRIO
   #define STEP_TIMER_IRQ_PRIO 2
 #endif
   #define TEMP_TIMER_IRQ_PRIO 14   // 14 = after hardware ISRs
 #endif
 
+#if HAS_TMC_SW_SERIAL
+  #include <SoftwareSerial.h>
+  #ifndef SWSERIAL_TIMER_IRQ_PRIO
+    #define SWSERIAL_TIMER_IRQ_PRIO 1
+  #endif
+#endif
+
 #ifdef STM32F0xx
   #define HAL_TIMER_RATE (F_CPU)      // Frequency of timer peripherals
   #define MCU_STEP_TIMER 16
   return nullptr;
 }
 
+void SetSoftwareSerialTimerInterruptPriority() {
+  TERN_(HAS_TMC_SW_SERIAL, SoftwareSerial::setInterruptPriority(SWSERIAL_TIMER_IRQ_PRIO, 0));
+}
+
 #endif // ARDUINO_ARCH_STM32 && !STM32GENERIC

Marlin/src/HAL/STM32/timers.h

 void HAL_timer_disable_interrupt(const uint8_t timer_num);
 bool HAL_timer_interrupt_enabled(const uint8_t timer_num);
 
+// Exposed here to allow all timer priority information to reside in timers.cpp
+void SetSoftwareSerialTimerInterruptPriority();
+
 //TIM_TypeDef* HAL_timer_device(const uint8_t timer_num); no need to be public for now. not public = not used externally
 
 // FORCE_INLINE because these are used in performance-critical situations

buildroot/share/tests/BIGTREE_BTT002-tests

 restore_configs
 opt_set MOTHERBOARD BOARD_BTT_BTT002_V1_0
 opt_set SERIAL_PORT 1
-exec_test $1 $2 "BigTreeTech BTT002 Default Configuration"
+opt_set X_DRIVER_TYPE TMC2209
+opt_set Y_DRIVER_TYPE TMC2130
+exec_test $1 $2 "BigTreeTech BTT002 Default Configuration plus TMC steppers"
 
 # clean up
 restore_configs

buildroot/share/tests/BIGTREE_SKR_PRO-tests

 opt_set E0_AUTO_FAN_PIN PC10
 opt_set E1_AUTO_FAN_PIN PC11
 opt_set E2_AUTO_FAN_PIN PC12
-exec_test $1 $2 "BigTreeTech SKR Pro 3 Extruders with Auto-Fan"
+opt_set X_DRIVER_TYPE TMC2209
+opt_set Y_DRIVER_TYPE TMC2130
+exec_test $1 $2 "BigTreeTech SKR Pro 3 Extruders with Auto-Fan and mixed TMC drivers"
 
 # clean up
 restore_configs

platformio.ini

   -DHAVE_HWSERIAL3
   -DPIN_SERIAL2_RX=PD_6
   -DPIN_SERIAL2_TX=PD_5
+  -IMarlin/src/HAL/STM32
 build_unflags     = -std=gnu++11
 extra_scripts     = pre:buildroot/share/PlatformIO/scripts/generic_create_variant.py
-lib_ignore        = Adafruit NeoPixel, SailfishLCD, SlowSoftI2CMaster
+lib_ignore        = Adafruit NeoPixel, SailfishLCD, SlowSoftI2CMaster, SoftwareSerial
 src_filter        = ${common.default_src_filter} +<src/HAL/STM32>
 
 #