sched: Extend ftrace event to record boost and reason code

Add a new ftrace event to record changes to boost setting. Also extend
sched_task_load() ftrace event to record boost setting and reason code
passed to select_best_cpu(). This will be useful for debug purpose.

Change-Id: Idac72f86d954472abe9f88a8db184343b7730287
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>