MAGIC value for powerReason should be stored in RTC backup on Horus (#7096)

- Allows the radio main application to start correctly when coming from an app in RAM
- Refactoring of the `UNEXPECTED_SHUTDOWN()` process
- Saves the RTC battery as BACKUP RAM is not needed on normal shutdown
- On PWR OFF on an ALERT, the radio won't show the next alert before shutting down
- Bootloader flashable through the SD Manager

radio/src/keys.cpp

@@ -189,7 +189,7 @@ bool waitKeysReleased()
 #endif
 
   while (keyDown()) {
-    wdt_reset();
+    WDG_RESET();
 
 #if !defined(BOOT)
     if ((get_tmr10ms() - start) >= 300) {  // wait no more than 3 seconds