This commit is a part of preparation to perform allocation/release
of isochronous resources in pcm.hw_params/hw_free callbacks.

This commit splits out an operation to configure stream parameters into
pcm.hw_params callback. In pcm.prepare callback, establishing
connections and start isochronous contexts.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>