Input: add support for the Samsung S6SY761 touchscreen

The S6SY761 touchscreen is a capicitive multi-touch controller
for mobile use. It's connected with i2c at the address 0x48.

This commit provides a basic version of the driver which can
handle only initialization, touch events and power states.

The controller is controlled by a firmware which, in the version
I currently have, doesn't provide all the possible
functionalities mentioned in the datasheet.

Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/samsung,s6sy761.txt

@@ -0,0 +1,34 @@
+* Samsung S6SY761 touchscreen controller
+
+Required properties:
+- compatible		: must be "samsung,s6sy761"
+- reg			: I2C slave address, (e.g. 0x48)
+- interrupt-parent	: the phandle to the interrupt controller which provides
+			  the interrupt
+- interrupts		: interrupt specification
+- avdd-supply		: analogic power supply
+- vdd-supply		: power supply
+
+Optional properties:
+- touchscreen-size-x	: see touchscreen.txt. This property is embedded in the
+			  device. If defined it forces a different x resolution.
+- touchscreen-size-y	: see touchscreen.txt. This property is embedded in the
+			  device. If defined it forces a different y resolution.
+
+Example:
+
+i2c@00000000 {
+
+	/* ... */
+
+	touchscreen@48 {
+		compatible = "samsung,s6sy761";
+		reg = <0x48>;
+		interrupt-parent = <&gpa1>;
+		interrupts = <1 IRQ_TYPE_NONE>;
+		avdd-supply = <&ldo30_reg>;
+		vdd-supply = <&ldo31_reg>;
+		touchscreen-size-x = <4096>;
+		touchscreen-size-y = <4096>;
+	};
+};