msm: mdp: Move wfd state signalling into mdp driver

Previously the WFD driver was reponsible for signalling the
online/offline events to userspace listeners.  This led to redundant
notifications due to the manner in which the WFD driver is used. The
signalling is better purposed when done from MDP driver.

Change-Id: Ifffbacb565f8758b65139f7b0e32df0773247e2d
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>