msm: mdss: Move assertive display calculation to vsync

Assertive display calculations should be done every vsync to ensure
that the strength and backlight values are up to date. DSI command mode
panels are not supported currently.

Change-Id: If615ed1b48a496f39bf6780ea936d9bc31275415
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>