ASoC: OMAP: HDMI: Use the DSS audio interface

Instead of accessing the HDMI IP directly, the CPU DAI driver takes
advantage of the audio interface provided by the DSS device driver.
The ASoC driver will link the DSS audio functionality with ALSA by
calling the appropriate DSS device driver functions at the relevant
moments. For this, three new DAI operations are added: trigger, prepare
and shutdown operations.

At the moment, it is assumed that only one HDMI display is available
in the system, as it is the case in OMAP4. However, in the future,
one DAI for each HDMI display should be provided.

Signed-off-by: Ricardo Neri <ricardo.neri@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>