leds: ktd2692: add device tree bindings for ktd2692

This patch adds the device tree bindings for ktd2692 flash LEDs.
Add Optional properties of child node for Flash LED
Signed-off-by: Ingi Kim <ingi2.kim@samsung.com>
Acked-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Acked-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

Documentation/devicetree/bindings/leds/leds-ktd2692.txt

+* Kinetic Technologies - KTD2692 Flash LED Driver
+
+KTD2692 is the ideal power solution for high-power flash LEDs.
+It uses ExpressWire single-wire programming for maximum flexibility.
+
+The ExpressWire interface through CTRL pin can control LED on/off and
+enable/disable the IC, Movie(max 1/3 of Flash current) / Flash mode current,
+Flash timeout, LVP(low voltage protection).
+
+Also, When the AUX pin is pulled high while CTRL pin is high,
+LED current will be ramped up to the flash-mode current level.
+
+Required properties:
+- compatible : Should be "kinetic,ktd2692".
+- ctrl-gpios : Specifier of the GPIO connected to CTRL pin.
+- aux-gpios : Specifier of the GPIO connected to AUX pin.
+
+Optional properties:
+- vin-supply : "vin" LED supply (2.7V to 5.5V).
+  See Documentation/devicetree/bindings/regulator/regulator.txt
+
+A discrete LED element connected to the device must be represented by a child
+node - See Documentation/devicetree/bindings/leds/common.txt
+
+Required properties for flash LED child nodes:
+  See Documentation/devicetree/bindings/leds/common.txt
+- led-max-microamp : Minimum Threshold for Timer protection
+  is defined internally (Maximum 300mA).
+- flash-max-microamp : Flash LED maximum current
+  Formula : I(mA) = 15000 / Rset.
+- flash-max-timeout-us : Flash LED maximum timeout.
+
+Optional properties for flash LED child nodes:
+- label : See Documentation/devicetree/bindings/leds/common.txt
+
+Example:
+
+ktd2692 {
+	compatible = "kinetic,ktd2692";
+	ctrl-gpios = <&gpc0 1 0>;
+	aux-gpios = <&gpc0 2 0>;
+	vin-supply = <&vbat>;
+
+	flash-led {
+		label = "ktd2692-flash";
+		led-max-microamp = <300000>;
+		flash-max-microamp = <1500000>;
+		flash-max-timeout-us = <1835000>;
+	};
+};