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

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";

};