dt: bindings: lp8860: Add trigger binding to the lp8860

Add a default trigger optional node to the child node.
This will allow the driver to set the trigger for a backlight.

Signed-off-by: Dan Murphy <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Jacek Anaszewski <[e-mail]>

Documentation/devicetree/bindings/leds/leds-lp8860.txt

···
 
 Optional child properties:
 	- label : see Documentation/devicetree/bindings/leds/common.txt
+	- linux,default-trigger :
+	   see Documentation/devicetree/bindings/leds/common.txt
 
 Example:
 
···
 	led@0 {
 		reg = <0>;
 		label = "white:backlight";
+		linux,default-trigger = "backlight";
 	};
 }