msm: mdss: hdmi: Add support for CEC

CEC, Consumer Electronics Control, is a protocol that provides
high-level control functions between TV and source device. Add
support for configuring CEC block within HDMI Tx hw. Also implement
an interface to read/write CEC messages to sink device.

Change-Id: I9241383a7f928f85208054557f982db5c9d00764
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>