ARM: dts: imx28-evk: Enable touchscreen support

Provide 'lradc-touchscreen-wires' property to the LRADC driver, so that
touchscreen can be functional.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28-evk.dts

@@ -182,6 +182,7 @@
 			};
 
 			lradc@80050000 {
+				fsl,lradc-touchscreen-wires = <4>;
 				status = "okay";
 			};