msm: kgsl: add Simple GPU governor.

 * Original code and idea from @faux123.
 * Current commit has some custom changes:
   - added the load history buffer to filter
     spikes and average the GPU scaling.

Change-Id: Id79819a6894a4fe0b78558aef49eec0163700b91
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>

Conflicts:

	drivers/gpu/msm/kgsl_pwrscale_trustzone.c