efi/x86: Move UEFI Runtime Services wrappers to generic code

In order for other archs (such as arm64) to be able to reuse the virtual
mode function call wrappers, move them to drivers/firmware/efi/runtime-wrappers.c.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>