drm/msm/sde: Add support for AD4 manual strength

Add property for AD4 manual strength value and provide operation
to set AD4 manual strength level. The change also support AD4
manual mode in idle-power collapse.

Change-Id: I848321a3edcc15af435f1d990107f1270e8210d9
Signed-off-by: Xu Yang <yangxu@codeaurora.org>