x86_64: Consolidate tsc calibration

Move the TSC calibration code to tsc.c. Reimplement it so the
pm timer can be used as a reference as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>