msm: mdss: Unblock mdp PP features when AD calib mode is enabled

Assertive display calibration mode can co-exist with MDP based
post-processing features, only the backlight changes need to be
blocked when AD calibration mode is enabled.

Change-Id: I9c2932e4fa305a9d53cb4dcca11b877f298b4a23
Signed-off-by: Ping Li <pingli@codeaurora.org>