add resume support for hpet

[Nate Lawson]

Andrea Bittau wrote:
> When resuming, the timer needs to be reactivated.  Some boxes use hpet for their
> time of day and if hpet doesn't resume, the time of day never changes, screwing
> up the whole box.  I'm not sure if this is the correct way to do thing [do you
> need re-calibration?] but it seems to work for me.

Yes, that was correct.  No recalibration is necessary since the HPET is
not variable-rate.  I committed the patch, thanks.

-- 
Nate