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/gui/common/stdlcd/radio_power_meter.cpp

@@ -50,7 +50,7 @@ void menuRadioPowerMeter(event_t event)
     lcdRefresh();
     moduleState[g_moduleIdx].readModuleInformation(&reusableBuffer.moduleSetup.pxx2.moduleInformation, PXX2_HW_INFO_TX_ID, PXX2_HW_INFO_TX_ID);
     /* wait 1s to resume normal operation before leaving */
-    watchdogSuspend(1000);
+    watchdogSuspend(500 /*5s*/);
     RTOS_WAIT_MS(1000);
     return;
   }