x86/efi: Build our own EFI services pointer table

It's not possible to dereference the EFI System table directly when
booting a 64-bit kernel on a 32-bit EFI firmware because the size of
pointers don't match.

In preparation for supporting the above use case, build a list of
function pointers on boot so that callers don't have to worry about
converting pointer sizes through multiple levels of indirection.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

diff --cc arch/x86/boot/compressed/eboot.c
Simple merge

diff --cc arch/x86/boot/compressed/eboot.h
Simple merge

diff --cc arch/x86/boot/compressed/head_32.S
Simple merge

diff --cc arch/x86/boot/compressed/head_64.S
Simple merge

diff --cc drivers/firmware/efi/efi-stub-helper.c
Simple merge