dt-bindings: net: renesas, ether: Improve schema validation

- Remove pinctrl consumer properties, as they are handled by core
    dt-schema,
  - Document missing properties,
  - Document missing PHY child node,
  - Add "additionalProperties: false".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>