efi/libstub: arm: Omit arch specific config table matching array on arm64

On arm64, the EFI stub is built into the kernel proper, and so the stub
can refer to its symbols directly. Therefore, the practice of using EFI
configuration tables to pass information between them is never needed,
so we can omit any code consuming such tables when building for arm64.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>