msm: kgsl: Avoid glitch in GPU during power collapse

During GPU power collapse there is a possiblity of glitch.
Avoid this by mutually excluding SMMU operations during
GPU power collapse regulator disable. In addition to this
poll for regulators to be off to avoid glitch as per the
recommendation of hardware team.

Change-Id: I887c9d2ab84ef308b9523ea316a2617ea2a2c8ce
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>