dt-bindings: net: sun8i-emac: Convert the binding to a schemas

Switch our Allwinner H3 EMAC controller binding to a YAML schema to enable
the DT validation. Since that controller is based on a Synopsys IP, let's
add the validation to that schemas with a bunch of conditionals.

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