dt-bindings: net: macb: Add NP4 macb variant

Add NP4 macb SoC variant.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>