audio: Remove all inputs other than SCO

No physically attached inputs exist

Change-Id: Ic308d522faa999e665c804aeb250509015fb1993
audio: Add support for 48k sampling rate and set it as default

Change-Id: I61f8cdf8ca08d17a81e3e667e922e6cc3a225f65
audio: Enable minimal S/PDIF support

Run HDMI+SPDIF simultaneously if both are connected, or just S/PDIF
if HDMI is unavailable.

TODO:
A similar approach should be possible for the tas5713, but I need to
get the speakers to test it.

Change-Id: I7b5b9d7b3c12f9ed05fedec6219568fd3501f7b4