x86, nmi: Support NMI watchdog on newer AMD CPU families

CPU families 0x12, 0x14 and 0x15 support this functionality.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
LKML-Reference: <20100930123357.GC20545@loge.amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>