dt-bindings: Add binding for Sitronix ST7735R display panels

This adds a new device tree binding for Sitronix ST7735R display panels,
such as the Adafruit 1.8" TFT.
Signed-off-by: David Lechner <david@lechnology.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1514833336-22564-3-git-send-email-david@lechnology.com

Documentation/devicetree/bindings/display/sitronix,st7735r.txt

+Sitronix ST7735R display panels
+
+This binding is for display panels using a Sitronix ST7735R controller in SPI
+mode.
+
+Required properties:
+- compatible:	"jianda,jd-t18003-t01", "sitronix,st7735r"
+- dc-gpios:	Display data/command selection (D/CX)
+- reset-gpios:	Reset signal (RSTX)
+
+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)
+- backlight:	phandle of the backlight device attached to the panel
+
+Example:
+
+	backlight: backlight {
+		compatible = "gpio-backlight";
+		gpios = <&gpio 44 GPIO_ACTIVE_HIGH>;
+	}
+
+	...
+
+	display@0{
+		compatible = "jianda,jd-t18003-t01", "sitronix,st7735r";
+		reg = <0>;
+		spi-max-frequency = <32000000>;
+		dc-gpios = <&gpio 43 GPIO_ACTIVE_HIGH>;
+		reset-gpios = <&gpio 80 GPIO_ACTIVE_HIGH>;
+		rotation = <270>;
+		backlight = &backlight;
+	};