ASoC: wm8731: Convert DT bindings to YAML format

Convert the WM8731 DT bindings to YAML format, including addition of
documentation for the regulator and clock bindings which the driver has
had for some time but which were not covered in the bindings document.

Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220325153121.1598494-7-broonie@kernel.org


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