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/main.cpp

@@ -167,8 +167,8 @@ void checkEeprom()
 #else
 void checkEeprom()
 {
-#if defined(RAMBACKUP) && !defined(SIMU)
-  if (TIME_TO_RAMBACKUP()) {
+#if defined(RTC_BACKUP_RAM) && !defined(SIMU)
+  if (TIME_TO_BACKUP_RAM()) {
     rambackupWrite();
     rambackupDirtyMsk = 0;
   }
@@ -504,7 +504,7 @@ void perMain()
 
   event_t evt = getEvent(false);
 
-#if defined(RAMBACKUP)
+#if defined(RTC_BACKUP_RAM)
   if (globalData.unexpectedShutdown) {
     drawFatalErrorScreen(STR_EMERGENCY_MODE);
     return;