sched: Add new trace events

Add trace events for update_task_ravg(), update_history(), and
set_task_cpu(). These tracepoints are useful for monitoring the
per-task and per-runqueue demand statistics.

Change-Id: Ibec9f945074ff31d1fc1a76ae37c40c8fea8cda9
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>