x86, fixmap: add CONFIG_EFI

Impact: new fixmap allocation

FIX_EFI_IO_MAP_FIRST_PAGE is used only when EFI is enabled.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Acked-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>