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>;
	};
