omapdss: hdmi audio: Make header file independent of video/omapdss.h

Clean up the header files regarding to hdmi audio so the omap-hdmi-audio.h
file will only need to include the platform_data/omapdss.h file.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Mark Brown <broonie@kernel.org>
CC: Jyri Sarha <jsarha@ti.com>
CC: Liam Girdwood <liam.r.girdwood@linux.intel.com>