sched: Add sysctl to enable power aware scheduling

Add sysctl to enable energy awareness at runtime. This is useful for
performance/power tuning/measurements and debugging. In addition this
will match up with the Documentation/scheduler/sched-hmp.txt documentation.

Change-Id: I0a9185498640d66917b38bf5d55f6c59fc60ad5c
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>