dt-bindings: bus: Add documentation for Tegra210 ACONNECT

Add binding documentation for the Tegra ACONNECT bus that is part of the
Audio Processing Engine (APE) on Tegra210. The ACONNECT bus is used to
access devices within the APE subsystem. The APE is located in a
separate power domain and so accesses made to the ACONNECT require the
power domain to be enabled as well as some platform specific clocks.
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/bus/nvidia,tegra210-aconnect.txt

+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 {
+			...
+		};
+	};