media: ov7740: Document device tree bindings

* Omnivision OV7740 CMOS image sensor

The Omnivision OV7740 image sensor supports multiple output image

size, such as VGA, and QVGA, CIF and any size smaller. It also

supports the RAW RGB and YUV output formats.

The common video interfaces bindings (see video-interfaces.txt) should

be used to specify link to the image data receiver. The OV7740 device

node should contain one 'port' child node with an 'endpoint' subnode.

Required Properties:

- compatible:	"ovti,ov7740".

- reg:		I2C slave address of the sensor.

- clocks:	Reference to the xvclk input clock.

- clock-names:	"xvclk".

Optional Properties:

- reset-gpios: Rreference to the GPIO connected to the reset_b pin,

  if any. Active low with pull-ip resistor.

- powerdown-gpios: Reference to the GPIO connected to the pwdn pin,

  if any. Active high with pull-down resistor.

Endpoint node mandatory properties:

- remote-endpoint: A phandle to the bus receiver's endpoint node.

Example:

	i2c1: i2c@fc028000 {

		ov7740: camera@21 {

			compatible = "ovti,ov7740";

			reg = <0x21>;

			pinctrl-names = "default";

			pinctrl-0 = <&pinctrl_sensor_power &pinctrl_sensor_reset>;

			clocks = <&isc>;

			clock-names = "xvclk";

			assigned-clocks = <&isc>;

			assigned-clock-rates = <24000000>;

			reset-gpios = <&pioA 43 GPIO_ACTIVE_LOW>;

			powerdown-gpios = <&pioA 44 GPIO_ACTIVE_HIGH>;

			port {

				ov7740_0: endpoint {

					remote-endpoint = <&isc_0>;

				};

			};

		};

	};