As long as I investigate SCS.1m, this model reports to transfer/receive
PCM data channels/MIDI conformant data channels in tx/rx AMDTP packet.
There's a contradiction that this model actually has no analog/digital
capture port for PCM frames and no physical MIDI ports.

I guess that SCS.1d also has the contradiction. This model has no
analog/digital ports for PCM frames and no physical MIDI ports, thus it
requires no streaming functionality.

This commit adds some modification codes to handle the contradiction,
as much as possible. Unfortunately, this module adds one PCM playback
substream for SCS.1d so as SCS.1m.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>