msm: kgsl: Preemption cleanups

Remove some unused gpudev hooks and further segment the A4XX and
A5XX specific code into their respective areas.  Remove some bits
that are only applicable to 4XX from the 5XX side.

Change-Id: Ic0dedbadc324b979583d7a3998195bf15ac537f6
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>