msm: kgsl: Add GMU feature flag support

There are many different flavors of GMU/GPMU out there
and more coming in the near future. Split and define
what these features are. These feature flags come in very
handy when trying to figure out what the device is capable
of and what the device is configured to do (ie device tree
and adreno flag combinations).

Change-Id: I8d11029ca0c85e855ed6c3de911481ee79928387
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>