We don't need the result before next sleep time, so no reason to
additionally increase interrupt latency.
While there, remove extra PM ticks to microseconds conversion, making
C2/C3 sleep times look 4 times smaller than really. The conversion
is already done by AcpiGetTimerDuration(). Now I see reported sleep
times up to 0.5s, just as expected for planned 2 wakeups per second.
MFC after: 1 month