[media] Documentation: dt: Add binding documentation for S5K6A3 image sensor

This patch adds binding documentation for the Samsung S5K6A3(YX)
raw image sensor.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

Documentation/devicetree/bindings/media/samsung-s5k6a3.txt

+Samsung S5K6A3(YX) raw image sensor
+---------------------------------
+
+S5K6A3(YX) is a raw image sensor with MIPI CSI-2 and CCP2 image data interfaces
+and CCI (I2C compatible) control bus.
+
+Required properties:
+
+- compatible	: "samsung,s5k6a3";
+- reg		: I2C slave address of the sensor;
+- svdda-supply	: core voltage supply;
+- svddio-supply	: I/O voltage supply;
+- afvdd-supply	: AF (actuator) voltage supply;
+- gpios		: specifier of a GPIO connected to the RESET pin;
+- clocks	: should contain list of phandle and clock specifier pairs
+		  according to common clock bindings for the clocks described
+		  in the clock-names property;
+- clock-names	: should contain "extclk" entry for the sensor's EXTCLK clock;
+
+Optional properties:
+
+- clock-frequency : the frequency at which the "extclk" clock should be
+		    configured to operate, in Hz; if this property is not
+		    specified default 24 MHz value will be used.
+
+The common video interfaces bindings (see video-interfaces.txt) should be
+used to specify link to the image data receiver. The S5K6A3(YX) device
+node should contain one 'port' child node with an 'endpoint' subnode.
+
+Following properties are valid for the endpoint node:
+
+- data-lanes : (optional) specifies MIPI CSI-2 data lanes as covered in
+  video-interfaces.txt.  The sensor supports only one data lane.