ASoC: SOF: Add PM support

Add support for saving and restoring DSP context in D3 to host DDR.

The suspend callback includes: suspend all pcm's stream that are running,
send CTX_SAVE ipc, drop all ipc's, release trace dma and then
power off the DSP.

And the resume callback performs the following steps: load FW, run FW,
re-initialize trace, restore pipeline, restore the kcontrol values
and finally send the ctx restore ipc to the dsp.

The streams that are suspended are resumed by the ALSA resume trigger.
If the streams are paused during system suspend, they are marked
explicitly so they can be restored during PAUSE_RELEASE.

Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>