sched/walt: Improve the scheduler

This change is for general scheduler improvement.

Change-Id: I5fbadf248c0bfe27bc761686de7a925cec2e4163
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Sai Harshini Nimmala <snimmala@codeaurora.org>
[satyap@codeaurora.org: port to 5.4 and fix trivial merge conflicts]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>