Documentation: sound: add description of Intel HDaudio multi-links

Add description of 'Skylake' multi-link structure added in 2015 and
recent extensions to support SoundWire/DMIC/SSP interfaces.
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/20230404104127.5629-2-peter.ujfalusi@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/sound/hd-audio/index.rst

@@ -9,3 +9,4 @@ HD-Audio
    controls
    dp-mst
    realtek-pc-beep
+   intel-multi-link