dt-bindings: net: Convert GENET binding to YAML

Convert the GENET binding to YAML, leveraging brcm,unimac-mdio.yaml and
the standard ethernet-controller.yaml files.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211206180049.2086907-5-f.fainelli@gmail.com


Signed-off-by: Rob Herring <robh@kernel.org>