dt-bindings: msm/hdmi: Add HDMI PHY bindings

Add HDMI PHY bindings. Update the example to use HDMI PHY.

Added a missing power-domains property in the HDMI core bindings. Also,
simplified HDMI TX's DT node name in the example.

Cc: devicetree@vger.kernel.org
Cc: Rob Herring <robh@kernel.org>

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>