dt-bindings: net: bcmgenet: Document 7712 binding

7712 includes a GENETv5 adapter with an on-chip 10/100 16nm Ethernet PHY
which requires us to document that controller's integration specifically
for proper driver keying.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/brcm,bcmgenet.txt

@@ -2,7 +2,8 @@
 
 Required properties:
 - compatible: should contain one of "brcm,genet-v1", "brcm,genet-v2",
-  "brcm,genet-v3", "brcm,genet-v4", "brcm,genet-v5", "brcm,bcm2711-genet-v5".
+  "brcm,genet-v3", "brcm,genet-v4", "brcm,genet-v5", "brcm,bcm2711-genet-v5" or
+  "brcm,bcm7712-genet-v5".
 - reg: address and length of the register set for the device
 - interrupts and/or interrupts-extended: must be two cells, the first cell
   is the general purpose interrupt line, while the second cell is the