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

also removed some hardcoded values

Signed-off-by: Paul Reioux
<reioux@gmail.com>

Conflicts:

drivers/gpu/msm/kgsl_pwrscale_trustzone.c

Signed-off-by: faux123
<reioux@gmail.com>

idea is taken here -
https://github.com/rmbq/android_kernel_htc_msm8960/commit/845c9d18a7964041f7d426878a59eae4ae845029