msm: kgsl: Ensure GPU gdscs are off in SLUMBER and during hard reset

Poll gdsc status to ensure it's off before transitioning to
SLUMBER and during hard reset. This is needed to make sure
that next wake-up is indeed a fresh start and doesn't fail
(especially during recovery from fault) because of stale state.

Change-Id: I064038c59315a9b8aa10c7dd4a45354f0f5e5447
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>