Input: add support for Azoteq IQS550/572/525

This patch adds support for the Azoteq IQS550/572/525 family of
trackpad/touchscreen controllers.

The driver has been tested with an IQS550EV02 evaluation board. A
demonstration of the driver's capabilities is available here:

https://youtu.be/sRNNx4XZBts

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/iqs5xx.txt

@@ -0,0 +1,80 @@
+Azoteq IQS550/572/525 Trackpad/Touchscreen Controller
+
+Required properties:
+
+- compatible			: Must be equal to one of the following:
+				  "azoteq,iqs550"
+				  "azoteq,iqs572"
+				  "azoteq,iqs525"
+
+- reg				: I2C slave address for the device.
+
+- interrupts			: GPIO to which the device's active-high RDY
+				  output is connected (see [0]).
+
+- reset-gpios			: GPIO to which the device's active-low NRST
+				  input is connected (see [1]).
+
+Optional properties:
+
+- touchscreen-min-x		: See [2].
+
+- touchscreen-min-y		: See [2].
+
+- touchscreen-size-x		: See [2]. If this property is omitted, the
+				  maximum x-coordinate is specified by the
+				  device's "X Resolution" register.
+
+- touchscreen-size-y		: See [2]. If this property is omitted, the
+				  maximum y-coordinate is specified by the
+				  device's "Y Resolution" register.
+
+- touchscreen-max-pressure	: See [2]. Pressure is expressed as the sum of
+				  the deltas across all channels impacted by a
+				  touch event. A channel's delta is calculated
+				  as its count value minus a reference, where
+				  the count value is inversely proportional to
+				  the channel's capacitance.
+
+- touchscreen-fuzz-x		: See [2].
+
+- touchscreen-fuzz-y		: See [2].
+
+- touchscreen-fuzz-pressure	: See [2].
+
+- touchscreen-inverted-x	: See [2]. Inversion is applied relative to that
+				  which may already be specified by the device's
+				  FLIP_X and FLIP_Y register fields.
+
+- touchscreen-inverted-y	: See [2]. Inversion is applied relative to that
+				  which may already be specified by the device's
+				  FLIP_X and FLIP_Y register fields.
+
+- touchscreen-swapped-x-y	: See [2]. Swapping is applied relative to that
+				  which may already be specified by the device's
+				  SWITCH_XY_AXIS register field.
+
+[0]: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+[1]: Documentation/devicetree/bindings/gpio/gpio.txt
+[2]: Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt
+
+Example:
+
+	&i2c1 {
+		/* ... */
+
+		touchscreen@74 {
+			compatible = "azoteq,iqs550";
+			reg = <0x74>;
+			interrupt-parent = <&gpio>;
+			interrupts = <17 4>;
+			reset-gpios = <&gpio 27 1>;
+
+			touchscreen-size-x = <640>;
+			touchscreen-size-y = <480>;
+
+			touchscreen-max-pressure = <16000>;
+		};
+
+		/* ... */
+	};