DT: leds: Add led-sources property

Add a property for defining device outputs the LED
represented by the DT child node is connected to.
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Bryan Wu <cooloney@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

Documentation/devicetree/bindings/leds/common.txt

 Common leds properties.
 
+LED and flash LED devices provide the same basic functionality as current
+regulators, but extended with LED and flash LED specific features like
+blinking patterns, flash timeout, flash faults and external flash strobe mode.
+
+Many LED devices expose more than one current output that can be connected
+to one or more discrete LED component. Since the arrangement of connections
+can influence the way of the LED device initialization, the LED components
+have to be tightly coupled with the LED device binding. They are represented
+by child nodes of the parent LED device binding.
+
 Optional properties for child nodes:
+- led-sources : List of device current outputs the LED is connected to. The
+		outputs are identified by the numbers that must be defined
+		in the LED device binding documentation.
 - label : The label for this LED.  If omitted, the label is
   taken from the node name (excluding the unit address).
 
@@ -33,7 +46,8 @@ system-status {
 
 camera-flash {
 	label = "Flash";
+	led-sources = <0>, <1>;
 	max-microamp = <50000>;
 	flash-max-microamp = <320000>;
 	flash-timeout-us = <500000>;
-}
+};