Documentation/bindings: net: marvell-pp2: add the system controller

This patch documents the new marvell,system-controller property used by
the Marvell ppv2 network driver.
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Tested-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/marvell-pp2.txt

@@ -45,6 +45,7 @@ Optional properties (port):
                    be the name associated to the interrupts listed. Valid
                    names are: "tx-cpu0", "tx-cpu1", "tx-cpu2", "tx-cpu3",
 		   "rx-shared".
+- marvell,system-controller: a phandle to the system controller.
 
 Example for marvell,armada-375-pp2: