dt-bindings: Add binding for Ilitek ILI9225 display panels

This adds a new binding for display panels that use an Ilitek ILI9225
controller.

The "ilitek,ili9225-2.2in-176x220" device listed has no identification
markings whatsoever and an hour of googling turned up nothing, hence the use
of the size and resolution in the name instead of a model name.

An example of this nameless device can be found at:
https://github.com/Nkawu/TFT_22_ILI9225Signed-off-by: David Lechner <david@lechnology.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1511122328-31133-3-git-send-email-david@lechnology.com

Documentation/devicetree/bindings/display/ilitek,ili9225.txt

+Ilitek ILI9225 display panels
+
+This binding is for display panels using an Ilitek ILI9225 controller in SPI
+mode.
+
+Required properties:
+- compatible:	"ilitek,ili9225-2.2in-176x220"
+- rs-gpios:	Register select signal
+- reset-gpios:	Reset pin
+
+The node for this driver must be a child node of a SPI controller, hence
+all mandatory properties described in ../spi/spi-bus.txt must be specified.
+
+Optional properties:
+- rotation:	panel rotation in degrees counter clockwise (0,90,180,270)
+
+Example:
+	display@0{
+		compatible = "ilitek,ili9225-2.2in-176x220";
+		reg = <0>;
+		spi-max-frequency = <12000000>;
+		rs-gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>;
+		reset-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
+		rotation = <270>;
+	};