drm/msm/sde: Update AD backlight scale property name

Update AD backlight scale property name to be sunlight visibility
backlight scale, so that it can be used by either AD or LTM based
on the HW availability.

Change-Id: I488620bd2e83d7587ba63b0f90a36c9cd13fa485
Signed-off-by: Ping Li <pingli@codeaurora.org>