x86, mrst: add cpu type detection

Medfield is the follow-up of Moorestown, it is treated under the same
HW sub-architecture. However, we do need to know the CPU type in order
for some of the driver to act accordingly.
We also have different optimal clock configuration for each CPU type.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
LKML-Reference: <1274295685-6774-3-git-send-email-jacob.jun.pan@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>