msm: kgsl: suspend device when the display does off

This change saves leakage current when the display is
off. In scenerios where a user is listening to an mp3
this feature stops the GPU as soon as the display goes
off. The GPU is started again when the display comes
back. The feature also avoids the GPU resuming when a
email sync happens while the device is suspended.

Change-Id: I6f42aefec72848fc49cf4c71433d95a01fa3094d
Signed-off-by: Suman Tatiraju <sumant@codeaurora.org>