ALSA: hda: document state machine for hdac_streams

ALSA: hda: document state machine for hdac_streams

The code in this library is far from self-explanatory, hopefully this
state diagram reverse-engineered from the code will help others
understand the expected transitions.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Link: https://lore.kernel.org/r/20220919121041.43463-3-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>