sched_avg: add run queue averaging.

Add code to calculate the run queue depth of a cpu and iowait
depth of the cpu.

The scheduler calls in to sched_update_nr_prod whenever there
is a runqueue change. This function maintains the runqueue average
and the iowait of that cpu in that time interval.

Whoever wants to know the runqueue average is expected to call
sched_get_nr_running_avg periodically to get the accumulated
runqueue and iowait averages for all the cpus.

Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>
(cherry picked from commit 0299fcaaad80e2c0ac9aa583c95107f6edc27750)

Signed-off-by: Ram Kumar Chakravarthy Chebathini <rcheba@codeaurora.org>
(cherry picked from commit 5325d8a44f8296170cd8f42e245dd79f7b7347bf)

Change-Id: I92875789886c3f7c2457a063de4b3b6d8c893718
Signed-off-by: Sudhir Sharma <sudsha@codeaurora.org>