dt-bindings: sound: Convert Allwinner SPDIF binding to YAML

The Allwinner SoCs feature an SPDIF controller across multiple SoC
generations.

However, earlier generations were a bit simpler than the subsequent ones,
and for example would always have RX and TX capabilities, and no reset
lines.

In order to express this, let's create two YAML schemas instead of the free
form text we had before.

Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>