[Core] Add Reboot keycode to core (#15990)

platforms/chibios/bootloaders/stm32duino.c

@@ -21,3 +21,8 @@
 __attribute__((weak)) void bootloader_jump(void) {
     NVIC_SystemReset();
 }
+
+__attribute__((weak)) void mcu_reset(void) {
+    BKP->DR10 = RTC_BOOTLOADER_JUST_UPLOADED;
+    NVIC_SystemReset();
+}