dt-bindings: net: Document Broadcom SYSTEMPORT clocks

The Broadcom SYSTEMPORT adapters require the use of two clocks for
normal operations and during Wake-on-LAN, document those in the binding
document.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -20,6 +20,11 @@ Optional properties:
 - systemport,num-tier1-arb: number of tier 1 arbiters, an integer
 - systemport,num-txq: number of HW transmit queues, an integer
 - systemport,num-rxq: number of HW receive queues, an integer
+- clocks: When provided, must be two phandles to the functional clocks nodes of
+  the SYSTEMPORT block. The first phandle is the main SYSTEMPORT clock used
+  during normal operation, while the second phandle is the Wake-on-LAN clock.
+- clock-names: When provided, names of the functional clock phandles, first
+  name should be "sw_sysport" and second should be "sw_sysportwol".
 
 Example:
 ethernet@f04a0000 {