dt-bindings: mfd: Add A33 GPADC binding

Allwinner SoCs' GPADC Device Tree bindings

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The Allwinner SoCs all have an ADC that can also act as a thermal sensor

and sometimes as a touchscreen controller.

Required properties:

  - compatible: "allwinner,sun8i-a33-ths",

  - reg: mmio address range of the chip,

  - #thermal-sensor-cells: shall be 0,

  - #io-channel-cells: shall be 0,

Example:

	ths: ths@01c25000 {

		compatible = "allwinner,sun8i-a33-ths";

		reg = <0x01c25000 0x100>;

		#thermal-sensor-cells = <0>;

		#io-channel-cells = <0>;

	};

sun4i, sun5i and sun6i SoCs are also supported via the older binding:

sun4i resistive touchscreen controller

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Required properties:

 - compatible: "allwinner,sun4i-a10-ts", "allwinner,sun5i-a13-ts" or

   "allwinner,sun6i-a31-ts"

 - reg: mmio address range of the chip

 - interrupts: interrupt to which the chip is connected

 - #thermal-sensor-cells: shall be 0

Optional properties:

 - allwinner,ts-attached	 : boolean indicating that an actual touchscreen

				   is attached to the controller

 - allwinner,tp-sensitive-adjust : integer (4 bits)

				   adjust sensitivity of pen down detection

				   between 0 (least sensitive) and 15

				   (defaults to 15)

 - allwinner,filter-type	 : integer (2 bits)

				   select median and averaging filter

				   samples used for median / averaging filter

				   0: 4/2

				   1: 5/3

				   2: 8/4

				   3: 16/8

				   (defaults to 1)

Example:

	rtp: rtp@01c25000 {

		compatible = "allwinner,sun4i-a10-ts";

		reg = <0x01c25000 0x100>;

		interrupts = <29>;

		allwinner,ts-attached;

		#thermal-sensor-cells = <0>;

		/* sensitive/noisy touch panel */

		allwinner,tp-sensitive-adjust = <0>;

		allwinner,filter-type = <3>;

	};