As part of the i386 conversion to the generic timekeeping infrastructure, this
introduces a new tsc.c file.  The code in this file replaces the TSC
initialization, management and access code currently in timer_tsc.c (which
will be removed) that we want to preserve.

The code also introduces the following functionality:

o tsc_khz: like cpu_khz but stores the TSC frequency on systems that do not
  change TSC frequency w/ CPU frequency

o check/mark_tsc_unstable: accessor/modifier flag for TSC timekeeping
  usability

o minor cleanups to calibration math.

This patch also includes a one line __cpuinitdata fix from Zwane Mwaikambo.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>