efi/gop: Convert GOP structures to typedef and clean up some types

Use typedef for the GOP structures, in anticipation of unifying
32/64-bit code. Also use more appropriate types in the non-bitness
specific structures for the framebuffer address and pointers.

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/20191224151025.32482-4-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>