msm: kgsl: convert pwrscale framework to use devfreq

Convert the clock frequency scaling infrastructure to
be based on devfreq.

Change-Id: I1a60ba339db5715a8836b835bd1b29b46e151af6
Signed-off-by: Jeremy Gebben <jgebben@codeaurora.org>
Signed-off-by: Vladimir Razgulin <vrazguli@codeaurora.org>