Doc/DT: Add DT binding documentation for MIPI DPI Panel

Add DT binding documentation for MIPI DPI Panel.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Archit Taneja <archit@ti.com>
Cc: devicetree@vger.kernel.org

Documentation/devicetree/bindings/video/panel-dpi.txt

+Generic MIPI DPI Panel
+======================
+
+Required properties:
+- compatible: "panel-dpi"
+
+Optional properties:
+- label: a symbolic name for the panel
+- enable-gpios: panel enable gpio
+
+Required nodes:
+- "panel-timing" containing video timings
+  (Documentation/devicetree/bindings/video/display-timing.txt)
+- Video port for DPI input
+
+Example
+-------
+
+lcd0: display@0 {
+        compatible = "samsung,lte430wq-f0c", "panel-dpi";
+        label = "lcd";
+
+        port {
+            lcd_in: endpoint {
+                    remote-endpoint = <&dpi_out>;
+            };
+        };
+
+        panel-timing {
+                clock-frequency = <9200000>;
+                hactive = <480>;
+                vactive = <272>;
+                hfront-porch = <8>;
+                hback-porch = <4>;
+                hsync-len = <41>;
+                vback-porch = <2>;
+                vfront-porch = <4>;
+                vsync-len = <10>;
+
+                hsync-active = <0>;
+                vsync-active = <0>;
+                de-active = <1>;
+                pixelclk-active = <1>;
+        };
+};