drm/msm: implement HDMI teardown sequence for DRM driver

Currently the teardown sequence in the DRM HDMI driver is
incorrect and it places the HDMI controller in an incorrect
state during cable unplug OR device teardown.
Fix the teardown sequence and follow the hardware programming
sequence correctly to avoid artifacts.

Change-Id: Ifb9ec303fa710409087a74c03435c83823d02763
Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>