msm: mdss: Move assertive display calculation to workqueue

Removes the possible case of delaying display_commit completion. AD_input
ioctl returns with last strength/backlight values calculated to aid in
management of AD feature from userspace.

Change-Id: I4c9a2941deece8f406b19b6b206c9fadf4f7250a
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>