This change adds the skew_consistency test, which twists the
ADJ_FREQUENCY knob back and forth and watches for timekeeping
inconsistencies.

Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Tested-by: NPrarit Bhargava <prarit@redhat.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>