Simple Framebuffer

A simple frame-buffer describes a raw memory region that may be rendered to,
with the assumption that the display hardware has already been set up to scan
out from that buffer.

Required properties:
- compatible: "simple-framebuffer"
- reg: Should contain the location and size of the framebuffer memory.
- width: The width of the framebuffer in pixels.
- height: The height of the framebuffer in pixels.
- stride: The number of bytes in each line of the framebuffer.
- format: The format of the framebuffer surface. Valid values are:
  - r5g6b5 (16-bit pixels, d[15:11]=r, d[10:5]=g, d[4:0]=b).
  - a8b8g8r8 (32-bit pixels, d[31:24]=a, d[23:16]=b, d[15:8]=g, d[7:0]=r).

Example:

	framebuffer {
		compatible = "simple-framebuffer";
		reg = <0x1d385000 (1600 * 1200 * 2)>;
		width = <1600>;
		height = <1200>;
		stride = <(1600 * 2)>;
		format = "r5g6b5";
	};