ASoC: SOF: pm: Introduce DSP power states

ASoC: SOF: pm: Introduce DSP power states

Add a new enum sof_dsp_power_states for all the possible
the DSP device states. The SOF driver currently handles
only the D0 and D3 states and support for other states
will be added later as needed.

Also, add a helper to determine the target DSP power state
based on the system suspend target.
The snd_sof_dsp_d0i3_on_suspend() function is renamed to
snd_sof_stream_suspend_ignored() to be more indicative
of what it does and it used to determine the target
DSP state during system suspend.

Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200129220726.31792-5-pierre-louis.bossart@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>