efi: x86: move efi_is_table_address() into arch/x86

The function efi_is_table_address() and the associated array of table
pointers is specific to x86. Since we will be adding some more x86
specific tables, let's move this code out of the generic code first.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>