The sm8250 audio driver uses the common Qualcomm device tree parser and
therefore already supports the "aux-devs" property that allows adding
additional auxiliary devices to the sound card (e.g. analog speaker
amplifiers that can be connected using "audio-routing").

Document the property in the DT schema for sm8250 as well. The description
is taken from simple-card.yaml which has a very similar property.

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211202145505.58852-3-stephan@gerhold.netSigned-off-by: Mark Brown <broonie@kernel.org>