efi: Conflict efi_loader with different stub bitness

efi: Conflict efi_loader with different stub bitness

We have 2 users of the EFI headers: efi_loader and the EFI stub. Efi_loader
always expects that the bitness of the definitions it uses is identical to
the execution.

The EFI stub however allows to run x86_64 U-Boot on 32bit EFI and the other
way around, so it allows for different bitness of EFI definitions and U-Boot
environment.

This patch explicitly requests via Kconfig that efi_loader can only be enabled
if the bitness is identical. Because we can run efi_loader on x86_64 without
EFI stub enabled, it also ensures that this case propagates the correct ABI
constraints.

Signed-off-by: Alexander Graf <agraf@suse.de>