Impact: New register definitions only

CMCI means support for raising an interrupt on a corrected machine
check event instead of having to poll for it. It's a new feature in
Intel Nehalem CPUs available on some machine check banks.

For details see the IA32 SDM Vol3a 14.5

Define the registers for it as a preparation for further patches.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>