[ALSA] Clean up PCM codes (take 2)

- Clean up initialization and destruction of substream instance
  Now snd_pcm_open_substream() alone does most initialization jobs.
  Add pcm_release callback for cleaning up at snd_pcm_release_substream()
- Tidy up PCM oss code

Signed-off-by: Takashi Iwai <tiwai@suse.de>
6 files changed