sched/walt: Improve the scheduler

This change is for general scheduler improvement.

Change-Id: I33e9ec890f8b54d673770d5d02dba489a8e08ce7
Signed-off-by: Sai Harshini Nimmala <snimmala@codeaurora.org>
[satyap@codeaurora.org: port to 5.4 and resolve trivial merge conflicts]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>