ASoC: OMAP: HDMI: Improve how the display state is verified

Before starting to play audio, we need to make sure that the
display is active and the current video mode supports audio. instead
of using the overlay manager in the machine driver, we use the DSS audio
interface's audio_supported function. As we already have a pointer to
the correct dssdev, we do not have to look for it every time audio is
to be played. Also, the CPU DAI startup function is called earlier
than the card hw_param function. Hence and we can detect the state of
the display earlier.

While there, add a error message if the constraint cannot be applied.

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

squash to improve err
Signed-off-by: Liam Girdwood <lrg@ti.com>