ASoC: omap-hdmi-audio: Add platform device for OMAP HDMI audio support

The platform device should only be registered from OMAPDSS HDMI
driver. The platform driver registers and unregisters all ASoC
components needed for OMAP HDMI audio.

The hdmi audio driver implements cpu-dai component using the callbacks
provided by OMAPDSS and registers the component under DSS HDMI
device. Omap-pcm is registered for platform component also under DSS
HDMI device. Dummy codec is used as as codec component. The hdmi audio
driver implements also the card and registers it under its own
platform device.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>