drm/bridge: anx7625: add HDMI audio function

Add audio HDMI codec function support, enable it through device true
flag "analogix,audio-enable".

Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211104033857.2634562-1-xji@analogixsemi.com