msm: mdss: Add separate backlight notify update for AD attenuation

Currently, there is only one type of backlight notification for
post-processing and it is completed only when AD is enabled and the
AD attenuated backlight changes. The PPDaemon needs a notification
for general backlight updates for CABL. This change adds separate
backlight notify updates for AD attenuated bl changes and regular
bl changes.

Change-Id: Ie35cdcf3f9f58d9678774e0d976c662fc4ea739f
Signed-off-by: Benet Clark <benetc@codeaurora.org>