ASoC: dt-bindings: Add audio-iio-aux

Industrial I/O devices can be present in the audio path.
These devices needs to be viewed as audio components in order to be
fully integrated in the audio path.

audio-iio-aux allows to consider these Industrial I/O devices as
auxliary audio devices.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Christophe Leroy <christophe.leroy@©sgroup.eu>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20230623085830.749991-2-herve.codina@bootlin.com


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