Convert the dmic-codec binding to DT schema format.

The '#sound-dai-cells' and 'sound-name-prefix' properties were not
documented, but are in use, so add them.
Reviewed-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221021175721.4005601-1-robh@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>