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

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

Marlin/src/gcode/gcode_d.cpp

@@ -30,6 +30,7 @@
   #include "../HAL/shared/eeprom_if.h"
   #include "../HAL/shared/Delay.h"
   #include "../sd/cardreader.h"
+  #include "../MarlinCore.h" // for kill
 
   extern void dump_delay_accuracy_check();
 
@@ -44,12 +45,16 @@
     switch (dcode) {
 
       case -1:
-        for (;;); // forever
+        for (;;) { /* loop forever (watchdog reset) */ }
 
       case 0:
         HAL_reboot();
         break;
 
+      case 10:
+        kill(PSTR("D10"), PSTR("KILL TEST"), parser.seen('P'));
+        break;
+
       case 1: {
         // Zero or pattern-fill the EEPROM data
         #if ENABLED(EEPROM_SETTINGS)