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"
  "mixer0-lcd0"
  "mixer0-lcd0-hdmi"
  "mixer1-lcd1-hdmi"
  "mixer1-lcd1-tve"

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>;
	};
};