DO NOT MERGE: Add SendMessageCallback to Hdmi control service.

As we have separate IO thread, we should have async callback
mechanism to get result of send request.
For that, I added SendMessageCallback interface to HdmiControl
Service
Along with this, replace message-based IO handling with
post Runnable based one for consistency

Change-Id: I61cf5b751b4f2af3b34956060869f3512f161d11