dt-bindings: net: convert rockchip-dwmac to json-schema

Convert Rockchip dwmac controller dt-bindings to YAML.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: David S. Miller <davem@davemloft.net>