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

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

Marlin/src/HAL/DUE/HAL.cpp

@@ -77,6 +77,8 @@ uint8_t HAL_get_reset_source() {
   }
 }
 
+void HAL_reboot() { rstc_start_software_reset(RSTC); }
+
 void _delay_ms(const int delay_ms) {
   // Todo: port for Due?
   delay(delay_ms);

Marlin/src/HAL/DUE/HAL.h

@@ -113,7 +113,7 @@ void sei();                     // Enable interrupts
 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