ASoC: SOF: Intel: hda-mlink: add helper to retrieve eml_lock

ASoC: SOF: Intel: hda-mlink: add helper to retrieve eml_lock

For SoundWire usages, we need to use the global eml_lock to
serialize/protect all accesses to shared registers.  Due to the split
implementation across two subsystems, we need to pass a pointer
around.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20230404104127.5629-19-peter.ujfalusi@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>