Adds optional property "hdmi-codec".

If specified, the machine driver should:
- Exposes a device that can write audio data to the DP bridge.
- Detects jack plug events.
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Link: https://lore.kernel.org/r/20210120080850.699354-5-tzungbi@google.comSigned-off-by: Mark Brown <broonie@kernel.org>