PerformanceControl: Turn it into a fragment and remove SU dependency

We do this to integrate it into our Settings app. Also, since we are
running as a System app, we don't need to go through a SU process
to run the commands, we can just write to files directly.
This avoids the big "SUPERUSER REQUEST" dialog.

Change-Id: If0d0b2f3c77faf6353c715105357b314637a6d72