imx: add SPDIF audio support

although some issues....
voodoo@debian:~$ dmesg | grep spdif
[    3.042392] imx-spdif sound-spdif.15: ASoC: CPU DAI (null) not registered
[    3.049338] imx-spdif sound-spdif.15: snd_soc_register_card failed: -517
[    3.056198] platform sound-spdif.15: Driver imx-spdif requests probe deferral

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>