Prepare mce.h for unification, so that it will build on 32-bit x86
kernels too.

[ Impact: cleanup ]
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>