drm/msm/gpu: Increase the pm runtime autosuspend for 5xx

Experimentation shows that resuming power quickly after suspending
ends up forcing a system hang for unknown reasons on 5xx targets.
To avoid cycling the power too much (especially during init)
turn up the autosuspend time for a5xx to 250ms and use
pm_runtime_put_autosuspend() when applicable.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>