ASoC: imx-hdmi: Add support for HBR/HD bitstreaming

This adds HBR passthrough support, required for HD audio bitstreaming of TrueHD and DTS-HD MA.

Proper application support requires having a correct ```/usr/share/alsa/cards/imx-hdmi-soc.conf``` which allows setting AESx parameters by the device name.

I've put example files here (the ```imx-spdif.conf``` is just for S/PDIF of course, adding the proper iec958 ALSA alias and AESx support there as well):
http://onse.fi/files/cubox/imx-hdmi-soc.conf
http://onse.fi/files/cubox/imx-spdif.conf

Tested quite lightly and with aplay/speaker-test only.

Of note is that I encountered frequent underruns during testing, but this happened with e.g. ```speaker-test -D hw:1,0 -f S16_LE -r 192000 -c 8``` as well so it is not a HBR-specific issue.