dt-bindings: simplefb-sunxi: Add sunxi simplefb extensions

If pre-filled framebuffer nodes are used, the firmware may need extra
properties to find the right node. This documents the properties to use
for this on sunxi platforms.
Signed-off-by: NHans de Goede <hdegoede@redhat.com>
Acked-by: NGrant Likely <grant.likely@linaro.org>
Signed-off-by: NTomi Valkeinen <tomi.valkeinen@ti.com>

Documentation/devicetree/bindings/video/simple-framebuffer-sunxi.txt

+Sunxi specific Simple Framebuffer bindings
+
+This binding documents sunxi specific extensions to the simple-framebuffer
+bindings. The sunxi simplefb u-boot code relies on the devicetree containing
+pre-populated simplefb nodes.
+
+These extensions are intended so that u-boot can select the right node based
+on which pipeline is being used. As such they are solely intended for
+firmware / bootloader use, and the OS should ignore them.
+
+Required properties:
+- compatible: "allwinner,simple-framebuffer"
+- allwinner,pipeline, one of:
+  "de_be0-lcd0"
+  "de_be1-lcd1"
+  "de_be0-lcd0-hdmi"
+  "de_be1-lcd1-hdmi"
+
+Example:
+
+chosen {
+	#address-cells = <1>;
+	#size-cells = <1>;
+	ranges;
+
+	framebuffer@0 {
+		compatible = "allwinner,simple-framebuffer", "simple-framebuffer";
+		allwinner,pipeline = "de_be0-lcd0-hdmi";
+		clocks = <&pll5 1>, <&ahb_gates 36>, <&ahb_gates 43>,
+			 <&ahb_gates 44>;
+		status = "disabled";
+	};
+};