ALSA: virtuoso: add S/PDIF input support for all Xonars

All Xonar cards support S/PDIF input, but the cards without optical or
coaxial plugs have only undocumented pin connectors.  Support for the
ST/STX was already added in a previous patch; this adds support for the
D1/DX (JP2), DG (J5), DS (J5), and HDAV Slim (J12).

Many thanks to Zoltan Miklos for testing the DS and DX.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>