msm: kgsl: Use cold boot only for the GMU

To ensure that state is correctly retained,
only use cold boot for the GMU for now.
Warm boot can be added as an option later
as an optimization.

Change-Id: Ie98c7f98fd6c40f4c43961080cd39afed0fcda14
Signed-off-by: Sushmita Susheelendra <ssusheel@codeaurora.org>
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>