ARM: mxs: Enable touchscreen on m28evk

This patch adds necessary DT properties to m28evk to enable touchscreen
in the LRADC block. The M28EVK is shipped with 4-wire resistive touchscreen.
Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28-m28evk.dts

@@ -177,6 +177,7 @@ rtc: rtc@68 {
 
 			lradc@80050000 {
 				status = "okay";
+				fsl,lradc-touchscreen-wires = <4>;
 			};
 
 			duart: serial@80074000 {