sched: Add additional ftrace events

This patch adds two ftrace events:

sched_task_load -> records information of a task, such as scaled demand
sched_cpu_load  -> records information of a cpu, such as nr_running,
		   nr_big_tasks etc

This will be useful to debug HMP related task placement decisions by
scheduler.

Change-Id: If91587149bcd9bed157b5d2bfdecc3c3bf6652ff
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>