dt-bindings: net: dsa: qca8k: add LEDs definition example

Add LEDs definition example for qca8k Switch Family to describe how they
should be defined for a correct usage.

Signed-off-by: Christian Marangi <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/dsa/qca8k.yaml

···
   PHY it is connected to. In this config, an internal mdio-bus is registered and
   the MDIO master is used for communication. Mixed external and internal
   mdio-bus configurations are not supported by the hardware.
+  Each phy has at most 3 LEDs connected and can be declared
+  using the standard LEDs structure.
 
 properties:
   compatible:
···
 examples:
   - |
     #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/leds/common.h>
 
     mdio {
         #address-cells = <1>;
···
                     label = "lan1";
                     phy-mode = "internal";
                     phy-handle = <&internal_phy_port1>;
+
+                    leds {
+                        #address-cells = <1>;
+                        #size-cells = <0>;
+
+                        led@0 {
+                            reg = <0>;
+                            color = <LED_COLOR_ID_WHITE>;
+                            function = LED_FUNCTION_LAN;
+                            default-state = "keep";
+                        };
+
+                        led@1 {
+                            reg = <1>;
+                            color = <LED_COLOR_ID_AMBER>;
+                            function = LED_FUNCTION_LAN;
+                            default-state = "keep";
+                        };
+                    };
                 };
 
                 port@2 {