sched/walt: improve the scheduler

This change is for general scheduler improvement.

Change-Id: I01e6610bba2e8c66a628d6289eeed4e854264fdd
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>