trace: cpu_freq_switch: Add profiler for CPU frequency switch times

It is sometimes useful to profile how long CPU frequency switches
take, and traces have already been added for this purpose. Make
use of these and the trace_stat framework to generate statistical
histograms of frequency switch times in the following format:

 # cat /sys/kernel/debug/tracing/trace_stat/cpu_freq_switch
  CPU START_KHZ  END_KHZ COUNT AVG_US MIN_US MAX_US
    |         |        |     |      |      |      |
    0    384000  1512000     3   2787   1648   3418
    0    486000   384000     1   1129   1129   1129
    0   1458000   384000     1   3174   3174   3174
    0   1512000   384000     1   3265   3265   3265
    0   1512000   486000     1   3235   3235   3235
    0   1512000  1458000     1    213    213    213
    0   1512000  1512000     1      0      0      0

Profiling is disabled by default (since it does incur some
overhead). It can be enabled or re-disabled echoing 1 or 0
to /sys/kernel/debug/tracing/cpu_freq_switch_profile_enabled

Change-Id: I3ef7f9d681b7bd13bcaa031003b10312afe1aefe
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
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.

Change-Id: Id8cb2ecf0ed479f090a83ccb72dd59c53fa73e0c
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>