Device tree bindings for Zinitx BT541 touchscreen controller

Required properties:

 - compatible		: Should be "zinitix,bt541"
 - reg			: I2C address of the chip. Should be 0x20
 - interrupts		: Interrupt to which the chip is connected

Optional properties:

 - vdd-supply		: Analog power supply regulator on VCCA pin
 - vddo-supply		: Digital power supply regulator on VDD pin
 - zinitix,mode		: Mode of reporting touch points. Some modes may not work
			  with a particular ts firmware for unknown reasons. Available
			  modes are 1 and 2. Mode 2 is the default and preferred.

The touchscreen-* properties are documented in touchscreen.txt in this
directory.

Example:

	i2c@00000000 {
		/* ... */

		bt541@20 {
			compatible = "zinitix,bt541";
			reg = <0x20>;
			interrupt-parent = <&msmgpio>;
			interrupts = <13 IRQ_TYPE_EDGE_FALLING>;
			pinctrl-names = "default";
			pinctrl-0 = <&tsp_default>;
			vdd-supply = <&reg_vdd_tsp>;
			vddo-supply = <&pm8916_l6>;
			touchscreen-size-x = <540>;
			touchscreen-size-y = <960>;
			zinitix,mode = <2>;
		};

		/* ... */
	};