efi/gop: Unify 32/64-bit functions

Use efi_table_attr macro to deal with 32/64-bit firmware using the same
source code.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: James Morse <james.morse@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: https://lkml.kernel.org/r/20191224151025.32482-5-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>