x86, mce: unify

move mce_64.c => mce.c and glue it up in the Makefile.
Remove mce_32.c

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>