* Toradex Colibri VF50 Touchscreen driver

Required Properties:
- compatible must be toradex,vf50-touchscreen
- io-channels: adc channels being used by the Colibri VF50 module
    IIO ADC for Y-, X-, Y+, X+ connections
- xp-gpios: FET gate driver for input of X+
- xm-gpios: FET gate driver for input of X-
- yp-gpios: FET gate driver for input of Y+
- ym-gpios: FET gate driver for input of Y-
- interrupts: pen irq interrupt for touch detection, signal from X plate
- pinctrl-names: "idle", "default"
- pinctrl-0: pinctrl node for pen/touch detection, pinctrl must provide
    pull-up resistor on X+, X-.
- pinctrl-1: pinctrl node for X/Y and pressure measurement (ADC) state pinmux
- vf50-ts-min-pressure: pressure level at which to stop measuring X/Y values

Example:

	touchctrl: vf50_touchctrl {
		compatible = "toradex,vf50-touchscreen";
		io-channels = <&adc1 0>,<&adc0 0>,
				<&adc0 1>,<&adc1 2>;
		xp-gpios = <&gpio0 13 GPIO_ACTIVE_LOW>;
		xm-gpios = <&gpio2 29 GPIO_ACTIVE_HIGH>;
		yp-gpios = <&gpio0 12 GPIO_ACTIVE_LOW>;
		ym-gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
		interrupt-parent = <&gpio0>;
		interrupts = <8 IRQ_TYPE_LEVEL_LOW>;
		pinctrl-names = "idle","default";
		pinctrl-0 = <&pinctrl_touchctrl_idle>, <&pinctrl_touchctrl_gpios>;
		pinctrl-1 = <&pinctrl_touchctrl_default>, <&pinctrl_touchctrl_gpios>;
		vf50-ts-min-pressure = <200>;
	};