dt-bindings: net: document bcmgenet WoL interrupt

A third interrupt cell can be provided to optionally specify
the interrupt used for handling Wake on LAN events.

Typically the wake up handling uses a separate interrupt
controller, so the interrupts-extended property is used to
accommodate this.
Signed-off-by: Doug Berger <opendmb@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -4,9 +4,12 @@ Required properties:
 - compatible: should contain one of "brcm,genet-v1", "brcm,genet-v2",
   "brcm,genet-v3", "brcm,genet-v4".
 - reg: address and length of the register set for the device
-- interrupts: must be two cells, the first cell is the general purpose
-  interrupt line, while the second cell is the interrupt for the ring
-  RX and TX queues operating in ring mode
+- interrupts and/or interrupts-extended: must be two cells, the first cell
+  is the general purpose interrupt line, while the second cell is the
+  interrupt for the ring RX and TX queues operating in ring mode.  An
+  optional third interrupt cell for Wake-on-LAN can be specified.
+  See Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+  for information on the property specifics.
 - phy-mode: see ethernet.txt file in the same directory
 - #address-cells: should be 1
 - #size-cells: should be 1