dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

* STMicroelectronics Flexible Direct Memory Access Device Tree bindings

The FDMA is a general-purpose direct memory access controller capable of

supporting 16 independent DMA channels. It accepts up to 32 DMA requests.

The FDMA is based on a Slim processor which requires a firmware.

* FDMA Controller

Required properties:

- compatible	: Should be one of

		 - st,stih407-fdma-mpe31-11, "st,slim-rproc";

		 - st,stih407-fdma-mpe31-12, "st,slim-rproc";

		 - st,stih407-fdma-mpe31-13, "st,slim-rproc";

- reg		: Should contain an entry for each name in reg-names

- reg-names	: Must contain "slimcore", "dmem", "peripherals", "imem" entries

- interrupts	: Should contain one interrupt shared by all channels

- dma-channels	: Number of channels supported by the controller

- #dma-cells	: Must be <3>. See DMA client section below

- clocks	: Must contain an entry for each clock

See: Documentation/devicetree/bindings/clock/clock-bindings.txt

Example:

	fdma0: dma-controller@8e20000 {

		compatible = "st,stih407-fdma-mpe31-11", "st,slim-rproc";

		reg = <0x8e20000 0x8000>,

		      <0x8e30000 0x3000>,

		      <0x8e37000 0x1000>,

		      <0x8e38000 0x8000>;

		reg-names = "slimcore", "dmem", "peripherals", "imem";

		clocks = <&clk_s_c0_flexgen CLK_FDMA>,

			 <&clk_s_c0_flexgen CLK_EXT2F_A9>,

			 <&clk_s_c0_flexgen CLK_EXT2F_A9>,

			 <&clk_s_c0_flexgen CLK_EXT2F_A9>;

		interrupts = <GIC_SPI 5 IRQ_TYPE_NONE>;

		dma-channels = <16>;

		#dma-cells = <3>;

	};

* DMA client

Required properties:

- dmas: Comma separated list of dma channel requests

- dma-names: Names of the aforementioned requested channels

Each dmas request consists of 4 cells:

1. A phandle pointing to the FDMA controller

2. The request line number

3. A 32bit mask specifying (see include/linux/platform_data/dma-st-fdma.h)

 -bit 2-0: Holdoff value, dreq will be masked for

	0x0: 0-0.5us

	0x1: 0.5-1us

	0x2: 1-1.5us

 -bit 17: data swap

	0x0: disabled

	0x1: enabled

 -bit 21: Increment Address

	0x0: no address increment between transfers

	0x1: increment address between transfers

 -bit 22: 2 STBus Initiator Coprocessor interface

	0x0: high priority port

	0x1: low priority port

4. transfers type

 0 free running

 1 paced

Example:

	sti_uni_player2: sti-uni-player@2 {

		compatible = "st,sti-uni-player";

		status = "disabled";

		#sound-dai-cells = <0>;

		st,syscfg = <&syscfg_core>;

		clocks = <&clk_s_d0_flexgen CLK_PCM_2>;

		assigned-clocks = <&clk_s_d0_flexgen CLK_PCM_2>;

		assigned-clock-parents = <&clk_s_d0_quadfs 2>;

		assigned-clock-rates = <50000000>;

		reg = <0x8D82000 0x158>;

		interrupts = <GIC_SPI 86 IRQ_TYPE_NONE>;

		dmas = <&fdma0 4 0 1>;

		dai-name = "Uni Player #1 (DAC)";

		dma-names = "tx";

		st,uniperiph-id = <2>;

		st,version = <5>;

		st,mode = "PCM";

	};