Soft Reset via Serial or post-kill button click (#21652)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/HAL/SAMD51/HAL.cpp

@@ -436,6 +436,8 @@ uint8_t HAL_get_reset_source() {
 }
 #pragma pop_macro("WDT")
 
+void HAL_reboot() { NVIC_SystemReset(); }
+
 extern "C" {
   void * _sbrk(int incr);
 

Marlin/src/HAL/SAMD51/HAL.h

@@ -109,7 +109,7 @@ typedef int8_t pin_t;
 void HAL_clear_reset_source();  // clear reset reason
 uint8_t HAL_get_reset_source(); // get reset reason
 
-inline void HAL_reboot() {}  // reboot the board or restart the bootloader
+void HAL_reboot();
 
 //
 // ADC