Documentation: dtb: xgene: Add rxlos GPIO mapping

Signed-off-by: NQuan Nguyen <qnguyen@apm.com>
Signed-off-by: NIyappan Subramanian <isubramanian@apm.com>
Tested-by: NFushen Chen <fchen@apm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/apm-xgene-enet.txt

@@ -47,6 +47,9 @@ Optional properties:
 	    Valid values are between 0 to 7, that maps to
 	    273, 589, 899, 1222, 1480, 1806, 2147, 2464 ps
 	    Default value is 2, which corresponds to 899 ps
+- rxlos-gpios: Input gpio from SFP+ module to indicate availability of
+	       incoming signal.
+
 
 Example:
 	menetclk: menetclk {