dt-bindings: dmaengine: Add binding for Actions Semi Owl SoCs

* Actions Semi Owl SoCs DMA controller

This binding follows the generic DMA bindings defined in dma.txt.

Required properties:

- compatible: Should be "actions,s900-dma".

- reg: Should contain DMA registers location and length.

- interrupts: Should contain 4 interrupts shared by all channel.

- #dma-cells: Must be <1>. Used to represent the number of integer

              cells in the dmas property of client device.

- dma-channels: Physical channels supported.

- dma-requests: Number of DMA request signals supported by the controller.

                Refer to Documentation/devicetree/bindings/dma/dma.txt

- clocks: Phandle and Specifier of the clock feeding the DMA controller.

Example:

Controller:

                dma: dma-controller@e0260000 {

                        compatible = "actions,s900-dma";

                        reg = <0x0 0xe0260000 0x0 0x1000>;

                        interrupts = <GIC_SPI 57 IRQ_TYPE_LEVEL_HIGH>,

                                     <GIC_SPI 58 IRQ_TYPE_LEVEL_HIGH>,

                                     <GIC_SPI 59 IRQ_TYPE_LEVEL_HIGH>,

                                     <GIC_SPI 60 IRQ_TYPE_LEVEL_HIGH>;

                        #dma-cells = <1>;

                        dma-channels = <12>;

                        dma-requests = <46>;

                        clocks = <&clock CLK_DMAC>;

                };

Client:

DMA clients connected to the Actions Semi Owl SoCs DMA controller must

use the format described in the dma.txt file, using a two-cell specifier

for each channel.

The two cells in order are:

1. A phandle pointing to the DMA controller.

2. The channel id.

uart5: serial@e012a000 {

        ...

        dma-names = "tx", "rx";

        dmas = <&dma 26>, <&dma 27>;

        ...

};