[PATCH] x86_64: Use the extended RIP MSR for machine check reporting if available.

They are rumoured to be much more reliable than the RIP in the stack frame on
P4s.

This is a borderline case because the code is very simple.  Please note there
are no plans to add support for all the MCE register MSRs.

Cc: <venkatesh.pallipadi@intel.com>
Cc: <racing.guo@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>