dt-bindings: sound: Convert jz47*-codec doc to YAML

Convert ingenic,jz4740-codec.txt and ingenic,jz4725b-codec.txt to one
single ingenic,codec.yaml file, since they share the same binding.

Add the ingenic,jz4770-codec compatible string in the process.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20191224002708.1207884-1-paul@crapouillou.net


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