net/macb: Update DT bindings documentation

Add missing "cdns,at91sam9260-macb", "atmel,sama5d3-gem" and
"atmel,sama5d4-gem" compatible strings.
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Reviewed-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/macb.txt

@@ -2,10 +2,13 @@
 
 Required properties:
 - compatible: Should be "cdns,[<chip>-]{macb|gem}"
-  Use "cdns,at91sam9260-macb" Atmel at91sam9260 and at91sam9263 SoCs.
+  Use "cdns,at91sam9260-macb" for Atmel at91sam9 SoCs or the 10/100Mbit IP
+  available on sama5d3 SoCs.
   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".
+  Use "cdns,sama5d3-gem" for the Gigabit IP available on Atmel sama5d3 SoCs.
+  Use "cdns,sama5d4-gem" for the Gigabit IP available on Atmel sama5d4 SoCs.
 - reg: Address and length of the register set for the device
 - interrupts: Should contain macb interrupt
 - phy-mode: See ethernet.txt file in the same directory.