msm: mdss: hdmi: Cable connection status notification

Provide a callback machanism to all the modules registered
for HDMI cable notifications. The registered modules will be
notified everytime the cable is connected or disconnected.
The callback will be scheduled on global kernel workqueue.

Change-Id: I74630748448d8479b6e0cda6ccd148cbeae48a51
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>