Add an op in hdmi_codec_ops so codec driver can register callback
function to handle plug event.

Driver in DRM can use this callback function to report connector status.
Signed-off-by: NCheng-Yi Chiang <cychiang@chromium.org>
Link: https://lore.kernel.org/r/20190717083327.47646-2-cychiang@chromium.orgReviewed-by: NTzung-Bi Shih <tzungbi@google.com>
Signed-off-by: NMark Brown <broonie@kernel.org>