This commit adds a support for MIDI capture/playback

When MIDI substrams already start streaming and PCM substreams are going to
join at different sampling rate, streams are stopped once. Then sampling rate
is changed and streams are restarted.
Signed-off-by: NTakashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: NClemens Ladisch <clemens@ladisch.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>