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/bluetooth.cpp

@@ -762,11 +762,11 @@ const char * Bluetooth::flashFirmware(const char * filename)
   pausePulses();
 
   bluetoothInit(BLUETOOTH_BOOTLOADER_BAUDRATE, true); // normal mode
-  watchdogSuspend(1000);
+  watchdogSuspend(500 /*5s*/);
   RTOS_WAIT_MS(1000);
 
   bluetoothInit(BLUETOOTH_BOOTLOADER_BAUDRATE, false); // bootloader mode
-  watchdogSuspend(1000);
+  watchdogSuspend(500 /*5s*/);
   RTOS_WAIT_MS(1000);
 
   const char * result = doFlashFirmware(filename);
@@ -785,7 +785,7 @@ const char * Bluetooth::flashFirmware(const char * filename)
   drawProgressScreen(getBasename(filename), STR_MODULE_RESET, 0, 0);
 
   /* wait 1s off */
-  watchdogSuspend(1000);
+  watchdogSuspend(500 /*5s*/);
   RTOS_WAIT_MS(1000);
 
   state = BLUETOOTH_STATE_OFF;