x86, mce: Add a global MCE init helper

Add an early initcall (pre SMP) which sets up global MCE
functionality.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Cc: Andi Kleen <andi@firstfloor.org>
LKML-Reference: <1255689093-26921-2-git-send-email-borislav.petkov@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>