KGSL: make simple govenor a selectable option, co-exist with ondemand

also removed some hardcoded values

Signed-off-by: Paul Reioux <reioux@gmail.com>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>

Conflicts:
	drivers/gpu/msm/kgsl_pwrscale_trustzone.c