sched/walt: Improve the scheduler

Improve core_ctl tracing such that the necessary flags for
debugging eval_need are present in the trace, and so that
all returns go through the same tracepoint, unlocking, and
return functionality.

Change-Id: I61d5ab86ba7650bea77e4416b0ffa9a07869bbf3
Signed-off-by: Stephen Dickey <dickey@codeaurora.org>
Signed-off-by: Tengfei Fan <tengfeif@codeaurora.org>