msm: mdss: Notify backlight events for AD and regular BL together

Postprocessing userspace is a client of backlight notifications from
driver. There are two notifications exposed, one for AD BL attenuation
and one for regular backlight updates. Previously, the notification
would be for one type or the other. This change makes the notifications
occur together if both notifications are needed.

Change-Id: Ia5bc520a183106e1f9a876583cb3a17435be08ed
Signed-off-by: Benet Clark <benetc@codeaurora.org>