PPC: Make BookE FIT/WDT timers more lazy

PPC: Make BookE FIT/WDT timers more lazy

Today we fire FIT and WDT timer events every time the respective bit
position in TB flips from 0 -> 1.

However, there is no need to do this if the end result would be that
we're changing a TSR bit that is set to 1 to 1 again. No guest visible
change would have occured.

So whenever we see that the TSR bit to our timer is already set, don't
even bother to update the timer that would potentially fire it off.

However, we do need to make sure that we update our timer that notifies
us of the TB flip when the respective TSR bit gets unset. In that case
we do care about the flip and need to notify the guest again. So add
a callback into our timer handlers when TSR bits get unset.

This improves performance for me when the guest is busy processing things.

Signed-off-by: Alexander Graf <agraf@suse.de>
Message-id: 1385416015-22775-2-git-send-email-agraf@suse.de
Signed-off-by: Anthony Liguori <aliguori@amazon.com>