msm: kgsl: Leave the MMU clocks on with the rest of the GPU

It is no longer power efficient to independently enable and disable
the MMU clocks. We can safely enable and disable them with the rest
of the GPU clocks and take back the infrastructure needed to handle
the clocks.

Change-Id: Ic0dedbadc48095eada9c5fce6004475a2cb0f0a9
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>