Documentation: DT: Add binding documentation for NVIDIA ADMA

* NVIDIA Tegra Audio DMA (ADMA) controller

The Tegra Audio DMA controller that is used for transferring data

between system memory and the Audio Processing Engine (APE).

Required properties:

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

- reg: Should contain DMA registers location and length. This should be

  a single entry that includes all of the per-channel registers in one

  contiguous bank.

- interrupt-parent: Phandle to the interrupt parent controller.

- interrupts: Should contain all of the per-channel DMA interrupts in

  ascending order with respect to the DMA channel index.

- clocks: Must contain one entry for the ADMA module clock

  (TEGRA210_CLK_D_AUDIO).

- clock-names: Must contain the name "d_audio" for the corresponding

  'clocks' entry.

- #dma-cells : Must be 1. The first cell denotes the receive/transmit

  request number and should be between 1 and the maximum number of

  requests supported. This value corresponds to the RX/TX_REQUEST_SELECT

  fields in the ADMA_CHn_CTRL register.

Example:

adma: dma@702e2000 {

	compatible = "nvidia,tegra210-adma";

	reg = <0x0 0x702e2000 0x0 0x2000>;

	interrupt-parent = <&tegra_agic>;

	interrupts = <GIC_SPI 24 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 25 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 27 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 28 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 29 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 30 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 31 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 33 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 34 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 35 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 37 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 38 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 39 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 40 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 41 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 42 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 43 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 44 IRQ_TYPE_LEVEL_HIGH>,

		     <GIC_SPI 45 IRQ_TYPE_LEVEL_HIGH>;

	clocks = <&tegra_car TEGRA210_CLK_D_AUDIO>;

	clock-names = "d_audio";

	#dma-cells = <1>;

};