msm: kgsl: Disable power scaling

Power scaling is not currently supported. Disable it
to prevent instability.

Change-Id: Ia064fea48a36204f520144b1fb88cf866799d6a8
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>
Signed-off-by: Oleg Perelet <operelet@codeaurora.org>