[PATCH] hpet: allow shared interrupts

This patch adds support for shared HPET interrupts.

The driver previously acknowledged interrupts for both edge and level
interrupts, but didn't actually allow a shared interrupt in the latter case.

We use a new per-timer flag to save whether the timer's interrupt might be
shared, and use it to do the processing required for level interrupts only if
necessary.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Acked-by: Bob Picco <bob.picco@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>