ASoC: SOF: Activate runtime PM with SOF OF device

SOF boots the DSP at probe and keeps it up all the time.
With this change, after booting if no one is using the DSP
the SOF core will turn off the DSP to save power.

Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Paul Olaru <paul.olaru@nxp.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20200924151518.15841-2-daniel.baluta@oss.nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>