ACPI: idle: mark_tsc_unstable() at init-time, not run-time

The c2 and c3 idle handlers check tsc_halts_in_c()
after every time they return from idle.  Um, when?:-)

Move this check to init-time to remove the unnecessary
run-time overhead, and also to have the check complete before
the first entry into the idle handler.

ff69f2bb


(acpi: fix of pmtimer overflow that make Cx states time incorrect)
replaced the hard-coded use of the PM-timer inside idle,
with ktime_get_readl(), which possibly uses the TSC --
so it is now especially prudent to detect a broken TSC
before entering idle.

http://bugzilla.kernel.org/show_bug.cgi?id=13087

Signed-off-by: Len Brown <len.brown@intel.com>