x86, mce: add MSR read wrappers for easier error injection

This will be used by future patches to allow machine check error injection.
Right now it's a nop, except for adding some wrappers around the MSR reads.

This is early in the sequence to avoid too many conflicts.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>