Input: ad7879 - add SPI device tree binding example

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/ad7879.txt

@@ -52,3 +52,21 @@ 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>;
+	};