dt-bindings: bus: Add binding for the Allwinner MBUS controller

The MBUS controller drives the MBUS that other devices in the SoC will
use to perform DMA. It also has a register interface that allows to
monitor and control the bandwidth and priorities for masters on that
bus.
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/sunxi/sunxi-mbus.txt

+Allwinner Memory Bus (MBUS) controller
+
+The MBUS controller drives the MBUS that other devices in the SoC will
+use to perform DMA. It also has a register interface that allows to
+monitor and control the bandwidth and priorities for masters on that
+bus.
+
+Required properties:
+ - compatible: Must be one of:
+	- allwinner,sun5i-a13-mbus
+ - reg: Offset and length of the register set for the controller
+ - clocks: phandle to the clock driving the controller
+ - dma-ranges: See section 2.3.9 of the DeviceTree Specification
+ - #interconnect-cells: Must be one, with the argument being the MBUS
+   port ID
+
+Each device having to perform their DMA through the MBUS must have the
+interconnects and interconnect-names properties set to the MBUS
+controller and with "dma-mem" as the interconnect name.
+
+Example:
+
+mbus: dram-controller@1c01000 {
+	compatible = "allwinner,sun5i-a13-mbus";
+	reg = <0x01c01000 0x1000>;
+	clocks = <&ccu CLK_MBUS>;
+	dma-ranges = <0x00000000 0x40000000 0x20000000>;
+	#interconnect-cells = <1>;
+};
+
+fe0: display-frontend@1e00000 {
+	compatible = "allwinner,sun5i-a13-display-frontend";
+	...
+	interconnects = <&mbus 19>;
+	interconnect-names = "dma-mem";
+};