Honestly, all of this is hacky, somehow people implementing these APIs
never bothered to put modifiers in some other register to be returned.
The EFI people got a whole struct dedicated to returning what key is
pressed, and didn't even put the modifiers in it.
EFI actually did implement this with EFI_SIMPLE_TEXT_INPUT_EX_PROTOCOL,
the returned struct holds the modifier. I can implement this using that
protocol and int 16/AH=01h at a later date.
