Add debug parameter for snd-sof-pci.

One of the usages for this debug parameter to disable pm_runtime,
which can be useful for platform bringup, or keep the parent device
active while enabling pm_runtime for child devices (e.g. with
SoundWire or MFD). This can also be useful to measure suspend-resume
latencies or child devices.
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20191008164443.1358-5-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>