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

Add NP4 macb SoC variant.
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/macb.txt

@@ -4,6 +4,7 @@ Required properties:
 - compatible: Should be "cdns,[<chip>-]{macb|gem}"
   Use "cdns,at91sam9260-macb" for Atmel at91sam9 SoCs or the 10/100Mbit IP
   available on sama5d3 SoCs.
+  Use "cdns,np4-macb" for NP4 SoC devices.
   Use "cdns,at32ap7000-macb" for other 10/100 usage or use the generic form: "cdns,macb".
   Use "cdns,pc302-gem" for Picochip picoXcell pc302 and later devices based on
   the Cadence GEM, or the generic form: "cdns,gem".