msm: kgsl: Add support for tuning bus accesses for bus dcvs

If the tuning parameter is present in the devicetree, do not use a
floating water-mark approach for bus dcvs. This fixes an issue where
we upvote due to stalled cycles but never down vote even when stalled
cycles have receded below the threshold.

Change-Id: Ia799b33a31de1c5e4ff4ad5b3f30d4585ec85e3c
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>