loader.efi: efi_readkey_ex needs to key despite the shift status or toggle status

From UEFI specification 2.8, page 434:
"It should also be noted that certain input devices may not be able to produce
shift or toggle state information, and in those cases the high order bit in
the respective Toggle and Shift state fields should not be active."

But we still need to check for ScanCode and UnicodeChar.

PR: 242660
Reported by: Trond Endrestol
MFC after: 1 week