sched: Add trace events for WALT

These trace events allows to track various functions
for WALT enabled platforms.

Change-Id: I446bd762584fd32b4a24515152e2a2755abed74d
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
[satyap@codeaurora.org: updated commit text to reflect the change]
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>