sched/walt: Improve the scheduler

This change is for general scheduler improvement.

Change-Id: I5d89acdde73f5379d68ebc8513d0bbeaac128f5d
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>