efi: Add calling convention annotation to all prototypes

efi: Add calling convention annotation to all prototypes

UEFI mandates MS calling convention on x86_64, which was not supported
on GCC when UEFI support was first introduced into GRUB. However, now we
can use the ms_abi function type attribute to annotate functions and
function pointers as adhering to the MS calling convention, and the
compiler will generate the correct instruction sequence for us.

So let's add the appropriate annotation to all the function prototypes.
This will allow us to drop the special call wrappers in a subsequent patch.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>