ASoC: SOF: ipc4: implement pm ctx_save callback

ASoC: SOF: ipc4: implement pm ctx_save callback

Use the context save callback to power down the primary core which is used
by the firmware as an indication that the DSP is going to be turned off.

The IMR boot setup is done in response to the primary core power down.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20220610083549.16773-7-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>