dt-bindings: display: panel: Add support for Raydium RM67191 panel

Add dt-bindings documentation for Raydium RM67191 DSI panel.
Signed-off-by: Robert Chiras <robert.chiras@nxp.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1561550907-9733-2-git-send-email-robert.chiras@nxp.com

Documentation/devicetree/bindings/display/panel/raydium,rm67191.txt

+Raydium RM67171 OLED LCD panel with MIPI-DSI protocol
+
+Required properties:
+- compatible: 		"raydium,rm67191"
+- reg:			virtual channel for MIPI-DSI protocol
+			must be <0>
+- dsi-lanes:		number of DSI lanes to be used
+			must be <3> or <4>
+- port: 		input port node with endpoint definition as
+			defined in Documentation/devicetree/bindings/graph.txt;
+			the input port should be connected to a MIPI-DSI device
+			driver
+
+Optional properties:
+- reset-gpios:		a GPIO spec for the RST_B GPIO pin
+- v3p3-supply:		phandle to 3.3V regulator that powers the VDD_3V3 pin
+- v1p8-supply:		phandle to 1.8V regulator that powers the VDD_1V8 pin
+- width-mm:		see panel-common.txt
+- height-mm:		see panel-common.txt
+- video-mode:		0 - burst-mode
+			1 - non-burst with sync event
+			2 - non-burst with sync pulse
+
+Example:
+
+	panel@0 {
+		compatible = "raydium,rm67191";
+		reg = <0>;
+		pinctrl-0 = <&pinctrl_mipi_dsi_0_1_en>;
+		pinctrl-names = "default";
+		reset-gpios = <&gpio1 7 GPIO_ACTIVE_LOW>;
+		dsi-lanes = <4>;
+		width-mm = <68>;
+		height-mm = <121>;
+
+		port {
+			panel_in: endpoint {
+				remote-endpoint = <&mipi_out>;
+			};
+		};
+	};