Avoid flood of PIT interrupts while debugging an hvm guest.

Avoid flood of PIT interrupts while debugging an hvm guest.

This is rebased to the new PIT code now. It has the same logic as
earlier. PIT tries to catch up the missed timer ticks by injected all
the ticks one by one so that Guest time stays close to the wall clock.
But while debugging a hvm guest if you stop the guest by debugger and
then continue, the guest sees flood of interrupts compensating the
missed ticks for the stopped time. This patch just check if the guest is
being debugged, if yes then it does not try to catch up with the missed
ticks.

Signed-off-by: Nitin A Kamble <nitin.a.kamble@.intel.com>