HPET fixes for reg writes

HPET fixes for reg writes

This patch addresses the problems found by Andriy Gapon:

- The code was incorrectly overwriting the high order 32
  bits of the timer and hpet config registers. This didn't show up
  in testing because linux and windows use hpet in legacy mode,
  where the high order 32 bits (advertising available interrupts)
  of the timer config register are ignored, and the high order 32
  bits of the hpet config register are reserved and unused.

- The mask for level-triggered interrupts was off by a bit. (hpet
  doesn't currently support level-triggered interrupts).

In addition, I removed some unused #defines, and corrected the ioapic
interrupt values advertised. I'd set this up early in hpet development
and never went back to correct it, and no bugs resulted since linux and
windows use hpet in legacy mode where available interrupts are ignored.

Signed-off-by: Beth Kon <eak@us.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>