x86/tsc: Prepare warp test for TSC adjustment

To allow TSC compensation cross nodes its necessary to know in which
direction the TSC warp was observed. Return the maximum observed value on
the calling CPU so the caller can determine the direction later.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/20161119134017.970859287@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>