sched: bucketize CPU c-state levels

C-state aware scheduler takes note of wakeup latency of each c-state
level to determine whether to pack or wake up LPM CPU.  But it doesn't
distinguish small and large delta as it's inefficient for scheduler to
do so on its critical path.

Disregard wakeup latencies less than 64 us between different c-state
levels.  This reduces unnecessary task packing.

CRs-fixed: 1074879
Change-Id: Ib0cadbd390d1a0b6da3e39c98010cedb43e5bf60
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>