drm/msm/sde: Add support for AD4 BL scale calculate

The change adds support for calculating ad bl scale. Scale should be
calculated by formula:(ad_output_bl * max_ad_bl_scale) / ad_input_bl.

Change-Id: I05b7a2e5676d81c212b67b45497cd472ee7ff0f3
Signed-off-by: Yuchao Ma <yuchaom@codeaurora.org>