Register ASoC HDMI codec for audio functionality and adds device tree
binding for audio configuration.

With the registered HDMI codec the tda998x node can be used like a
regular codec node in ASoC card configurations. HDMI audio info-frame
and audio stream header is generated by the ASoC HDMI codec. The codec
also applies constraints for available sample-rates based on Edid Like
Data from the display. The device tree binding document has been
updated [1].

Part of this patch has been inspired by Jean Francoise's "drm/i2c: tda998x:
Add support of a DT graph of ports"-patch [2]. There may still be some
identical lines left from the original patch and some of the ideas
have come from there.

[1] Documentation/devicetree/bindings/display/bridge/tda998x.txt
[2] http://mailman.alsa-project.org/pipermail/alsa-devel/2015-July/095255.htmlSigned-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>