The state machine and notes don't accurately explain or allow
transitions from STREAM_DEPREPARED and STREAM_DISABLED.

Add more explanations and allow for more transitions as a result of a
trigger_stop(), trigger_suspend() and prepare(), depending on the
ALSA/ASoC layer behavior defined by the INFO_RESUME and INFO_PAUSE
flags.

Also add basic checks to help debug inconsistent states and illegal
state machine transitions.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200114235227.14502-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>