Input: ad7879 - add SPI device tree binding example

		adi,averaging = /bits/ 8 <1>;

		adi,conversion-interval = /bits/ 8 <255>;

	};

	ad7879@1 {

		compatible = "adi,ad7879";

		spi-max-frequency = <5000000>;

		reg = <1>;

		spi-cpol;

		spi-cpha;

		gpio-controller;

		interrupt-parent = <&gpio1>;

		interrupts = <13 IRQ_TYPE_EDGE_FALLING>;

		touchscreen-max-pressure = <4096>;

		adi,resistance-plate-x = <120>;

		adi,first-conversion-delay = /bits/ 8 <3>;

		adi,acquisition-time = /bits/ 8 <1>;

		adi,median-filter-size = /bits/ 8 <2>;

		adi,averaging = /bits/ 8 <1>;

		adi,conversion-interval = /bits/ 8 <255>;

	};