dt-bindings: Add docs for EL15203000

Add documentation and example for dt-bindings EL15203000.
LED board (aka RED LED board) from Crane Merchandising Systems.
Signed-off-by: Oleh Kravchenko <oleg@kaa.org.ua>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/leds/leds-el15203000.txt

+Crane Merchandising System - EL15203000 LED driver
+--------------------------------------------------
+
+This LED Board (aka RED LEDs board) is widely used in
+coffee vending machines produced by Crane Merchandising Systems.
+The board manages 3 LEDs and supports predefined blinking patterns
+for specific leds.
+
+Vending area LED encoded with symbol 'V' (hex code 0x56).
+Doesn't have any hardware blinking pattern.
+
+Screen light tube LED which surrounds vending machine screen and
+encoded with symbol 'S' (hex code 0x53). Supports blinking breathing pattern.
+
+Water Pipe LED encoded with symbol 'P' (hex code 0x50) and
+actually consists of 5 LEDs that exposed by protocol like one LED.
+Supports next patterns:
+- cascade pattern
+- inversed cascade pattern
+- bounce pattern
+- inversed bounce pattern
+
+Required properties:
+- compatible : "crane,el15203000"
+- #address-cells : must be 1
+- #size-cells : must be 0
+
+Property rules described in Documentation/devicetree/bindings/spi/spi-bus.txt
+apply. In particular, "reg" and "spi-max-frequency" properties must be given.
+
+Optional LED sub-node properties:
+- function:
+	see Documentation/devicetree/bindings/leds/common.txt
+- color:
+	see Documentation/devicetree/bindings/leds/common.txt
+
+Example
+-------
+
+#include <dt-bindings/leds/common.h>
+
+led-controller@0 {
+	compatible = "crane,el15203000";
+	reg = <0>;
+	spi-max-frequency = <50000>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	/* water pipe */
+	led@50 {
+		reg = <0x50>;
+		function = "pipe";
+		color = <LED_COLOR_ID_RED>;
+	};
+
+	/* screen frame */
+	led@53 {
+		reg = <0x53>;
+		function = "screen";
+		color = <LED_COLOR_ID_RED>;
+	};
+
+	/* vending area */
+	led@56 {
+		reg = <0x56>;
+		function = "vend";
+		color = <LED_COLOR_ID_RED>;
+	};
+};