sched/fair: Improve the scheduler

This change is for general scheduler improvement.

Change-Id: I9216f9316e2bad067c10762de8d67912826b7bc7
Signed-off-by: Maria Yu <aiquny@codeaurora.org>
Co-developed-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
[pkondeti@codeaurora.org: skip_cpu argument is implemented for fbt]
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>