ASoC: SOF: imx8: Add runtime PM / System PM support

Handle clocks and mailbox channels at runtime suspend/resume
in order to save power.

DSP runtime PM uses a timeout of 2s. If device
is idle for 2s system will enter runtime suspend.

Because SOF state machine assumes that even if the DSP wasn't previously
active at a System resume, will re-load the firmware we need to make sure
that all needed resources are active.

Kernel core will take care of enabling the PD, we need to make sure that
we request the MU channels.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20211119094319.81674-3-daniel.baluta@oss.nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>