Stanton SCS.1d doesn't support packet streaming even if it has plugs for
isochronous communication.

This commit is a preparation for this case. The 'has_input' member is
added to specific structure, and MIDI/PCM interfaces are not added when
the member is false.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20200113073418.24622-3-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>