x86/tsc_msr: Add Airmont reference clock values

per the Intel 64 and IA-32 Architecture Software Developer's Manual...

Add the reference clock for Intel Atom Processors
Based on the Airmont Microarchitecture.

Reported-by: Stephane Gasparini <stephane.gasparini@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/abc6a0f4b18281410da1a3f26e2819d8e03e144f.1466138954.git.len.brown@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>