sched/walt: improve the scheduler

This change is for general scheduler improvement.

Change-Id: Ia62cb98734eeabe1f045e6d3e2081b7c57366aaa
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
[clingutla@codeaurora.org: Resolved merge conflicts]
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>