[PATCH] x86: Add a cumulative thermal throttle event counter.

The counter is exported to /sys that keeps track of the
number of thermal events, such that the user knows how bad the
thermal problem might be (since the logging to syslog and mcelog
is rate limited).

AK: Fixed cpu hotplug locking

Signed-off-by: Dmitriy Zavin <dmitriyz@google.com>
Signed-off-by: Andi Kleen <ak@suse.de>