Meson specific Simple Framebuffer bindings

This binding documents meson specific extensions to the simple-framebuffer
bindings. The meson 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: "amlogic,simple-framebuffer", "simple-framebuffer"
- amlogic,pipeline, one of:
  "vpu-cvbs"
  "vpu-hdmi"

Example:

chosen {
	#address-cells = <2>;
	#size-cells = <2>;
	ranges;

	simplefb_hdmi: framebuffer-hdmi {
		compatible = "amlogic,simple-framebuffer",
			     "simple-framebuffer";
		amlogic,pipeline = "vpu-hdmi";
		clocks = <&clkc CLKID_HDMI_PCLK>,
			 <&clkc CLKID_CLK81>,
			 <&clkc CLKID_GCLK_VENCI_INT0>;
		power-domains = <&pwrc_vpu>;
	};
};