mcelog: Decode new simple error code number 6

Edition 050 of the Intel SDM released in late February 2014
includes a new simple error code in "Table 15-8. IA32_MCi_Status
[15:0] Simple Error Code Encoding".  Code 6 (0000 0000 0000 0110)
has been allocated for the reporting of cases where the BIOS SMM
code attempts to execute code outside of the protected SMRR area.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>