msm: kgsl: Add support for GPU AB voting

Enable AB voting for GPU using devfreq DDR bandwidth
voting driver. Now from the GPU side, there will be two
sets of votes. Kgsl will vote both AB and IB and GMU
will vote only IB.

Change-Id: I4cef2fbdc799ad8e87ecc63de858c214cbef270d
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>