DT: leds: Improve examples by adding some context

During my work on some new LED trigger I tried adding example similar to
the existing ones which received following comment from Rob:
> It's not really clear in the example this is an LED node as it is
> incomplete.

Keeping that in mind I suggest adding context for the existing example
entries in hope to make documentation more clear.

Signed-off-by: Rafał Miłecki <[e-mail]>
Signed-off-by: Jacek Anaszewski <[e-mail]>

Documentation/devicetree/bindings/leds/common.txt

···
 
 Examples:
 
-system-status {
-	label = "Status";
-	linux,default-trigger = "heartbeat";
-	...
+gpio-leds {
+	compatible = "gpio-leds";
+
+	system-status {
+		label = "Status";
+		linux,default-trigger = "heartbeat";
+		gpios = <&gpio0 0 GPIO_ACTIVE_HIGH>;
+	};
 };
 
-camera-flash {
-	label = "Flash";
-	led-sources = <0>, <1>;
-	led-max-microamp = <50000>;
-	flash-max-microamp = <320000>;
-	flash-max-timeout-us = <500000>;
+max77693-led {
+	compatible = "maxim,max77693-led";
+
+	camera-flash {
+		label = "Flash";
+		led-sources = <0>, <1>;
+		led-max-microamp = <50000>;
+		flash-max-microamp = <320000>;
+		flash-max-timeout-us = <500000>;
+	};
 };