loader.efi: fix panic() after BS off

panic() is using multiple services - attempting to read
keyboard, accessing time functions and finally, exiting the loader.

Protect all the accessed listed above. Note, when BS are off,
we really can not just exit the loader, we only can reboot.

(cherry-picked from commit a2e02d9d8e100bc41cf99b8fd04738954e48a94e)