x86/tsc: Add missing Cherrytrail frequency to the table

Intel Cherrytrail is based on Airmont core so MSR_FSB_FREQ[2:0] = 4
means that the CPU reference clock runs at 80MHz.  Add this missing
frequency to the table.

Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Link: http://lkml.kernel.org/r/87y47gty89.fsf@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>