Kexec kernel will use saved runtime virtual mapping, so add a new
function efi_map_region_fixed() for directly mapping a md to md->virt.

The md is passed in from 1st kernel, the virtual addr is saved in
md->virt_addr.
Signed-off-by: NDave Young <dyoung@redhat.com>
Acked-by: NBorislav Petkov <bp@suse.de>
Tested-by: NToshi Kani <toshi.kani@hp.com>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>