cpufreq: sched: update CPU utilization upon CFS task dequeue

At present, fair scheduler doesn't update CPU utilization when a
dequeue is due to preemption under the assumption it's undergoing
migration and CPU utilization will be updated once migration completed.
However it's not true always.  For example when task is actively
migrated stopper which is RT task enqueued and preempts current CFS
tasks and then migrates CFS tasks to other CPU which can be different
frequency domain.
Once migration finished context switches from stopper to idle task
no CFS utilization update requested OOP stays higher than actual need.

Fix such an error by requesting new OPP every time when a CFS task
dequeued.

Change-Id: I8906396995cd1b8f2b000e64e45ca2929d6ac9b1
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>