dt-bindings: bus: Add documentation for Tegra210 ACONNECT

NVIDIA Tegra ACONNECT Bus

The Tegra ACONNECT bus is an AXI switch which is used to connnect various

components inside the Audio Processing Engine (APE). All CPU accesses to

the APE subsystem go through the ACONNECT via an APB to AXI wrapper.

Required properties:

- compatible: Must be "nvidia,tegra210-aconnect".

- clocks: Must contain the entries for the APE clock (TEGRA210_CLK_APE),

  and APE interface clock (TEGRA210_CLK_APB2APE).

- clock-names: Must contain the names "ape" and "apb2ape" for the corresponding

  'clocks' entries.

- power-domains: Must contain a phandle that points to the audio powergate

  (namely 'aud') for Tegra210.

- #address-cells: The number of cells used to represent physical base addresses

  in the aconnect address space. Should be 1.

- #size-cells: The number of cells used to represent the size of an address

  range in the aconnect address space. Should be 1.

- ranges: Mapping of the aconnect address space to the CPU address space.

All devices accessed via the ACONNNECT are described by child-nodes.

Example:

	aconnect@702c0000 {

		compatible = "nvidia,tegra210-aconnect";

		clocks = <&tegra_car TEGRA210_CLK_APE>,

			 <&tegra_car TEGRA210_CLK_APB2APE>;

		clock-names = "ape", "apb2ape";

		power-domains = <&pd_audio>;

		#address-cells = <1>;

		#size-cells = <1>;

		ranges = <0x702c0000 0x0 0x702c0000 0x00040000>;

		status = "disabled";

		child1 {

			...

		};

		child2 {

			...

		};

	};