ASoC: dt-bindings: qcom: Document qcom,msm8916-qdsp6-sndcard compatible

ASoC: dt-bindings: qcom: Document qcom,msm8916-qdsp6-sndcard compatible

There are two possible audio setups on MSM8916/APQ8016: Normally the audio
is routed through the audio/modem DSP (covered by the qdsp6 driver). During
upstreaming for the DragonBoard 410c it was decided to bypass it and
instead talk directly to the audio controller using the "lpass" driver.

Bypassing the DSP gives more control about the audio configuration but limits
the functionality: For example, routing audio through the audio/modem DSP is
strictly required for voice call audio. Also, without the special changes in
the DB410c firmware other MSM8916 devices can only use the bypass as long as
the modem DSP is not started. Otherwise, the firmware will assume control of
the LPASS hardware block and audio is no longer functional.

Add support for using the DSP audio setup instead using a new
"qcom,msm8916-qdsp6-sndcard" compatible. It is basically a mixture of
the apq8016-sbc-sndcard and the newer sm8250-sndcard, which uses
indirect QDSP6 DAI links instead of the direct LPASS DAI links.

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211202145505.58852-5-stephan@gerhold.net
Signed-off-by: Mark Brown <broonie@kernel.org>