x86: Add UV EFI table entry v4

Look for a UV entry in the EFI tables.

Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Paul Jackson <pj@sgi.com>
Acked-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>