dt-bindings: display: Add King Display KD035G6-54NT panel documentation

The KD035G6-54NT is a 3.5" 320x240 24-bit TFT LCD panel.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190603152555.23527-1-paul@crapouillou.net

Documentation/devicetree/bindings/display/panel/kingdisplay,kd035g6-54nt.txt

+King Display KD035G6-54NT 3.5" (320x240 pixels) 24-bit TFT LCD panel
+
+Required properties:
+- compatible: should be "kingdisplay,kd035g6-54nt"
+- power-supply: See panel-common.txt
+- reset-gpios: See panel-common.txt
+
+Optional properties:
+- backlight: see panel-common.txt
+
+The generic bindings for the SPI slaves documented in [1] also apply.
+
+The device node can contain one 'port' child node with one child
+'endpoint' node, according to the bindings defined in [2]. This
+node should describe panel's video bus.
+
+[1]: Documentation/devicetree/bindings/spi/spi-bus.txt
+[2]: Documentation/devicetree/bindings/graph.txt
+
+Example:
+
+&spi {
+	panel@0 {
+		compatible = "kingdisplay,kd035g6-54nt";
+		reg = <0>;
+
+		spi-max-frequency = <3125000>;
+		spi-3wire;
+		spi-cs-high;
+
+		reset-gpios = <&gpe 2 GPIO_ACTIVE_LOW>;
+
+		backlight = <&backlight>;
+		power-supply = <&ldo6>;
+
+		port {
+			panel_input: endpoint {
+				remote-endpoint = <&panel_output>;
+			};
+		};
+	};
+};