dt-bindings: meson: add specific simplefb bindings

Similar to simple-framebuffer-sunxi, we support different display pipelines
that the firmware is free to choose from.

This documents the "amlogic,simple-framebuffer" compatible and the
"amlogic,pipeline" extension.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Jourdan <mjourdan@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

Documentation/devicetree/bindings/display/amlogic,simple-framebuffer.txt

+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>;
+	};
+};