* BCM2835 DMA controller

The BCM2835 DMA controller has 16 channels in total.
Only the lower 13 channels have an associated IRQ.
Some arbitrary channels are used by the firmware
(1,3,6,7 in the current firmware version).
The channels 0,2 and 3 have special functionality
and should not be used by the driver.

Required properties:
- compatible: Should be "brcm,bcm2835-dma".
- reg: Should contain DMA registers location and length.
- interrupts: Should contain the DMA interrupts associated
		to the DMA channels in ascending order.
- #dma-cells: Must be <1>, the cell in the dmas property of the
		client device represents the DREQ number.
- brcm,dma-channel-mask: Bit mask representing the channels
			 not used by the firmware in ascending order,
			 i.e. first channel corresponds to LSB.

Example:

dma: dma@7e007000 {
	compatible = "brcm,bcm2835-dma";
	reg = <0x7e007000 0xf00>;
	interrupts = <1 16>,
		     <1 17>,
		     <1 18>,
		     <1 19>,
		     <1 20>,
		     <1 21>,
		     <1 22>,
		     <1 23>,
		     <1 24>,
		     <1 25>,
		     <1 26>,
		     <1 27>,
		     <1 28>;

	#dma-cells = <1>;
	brcm,dma-channel-mask = <0x7f35>;
};

DMA clients connected to the BCM2835 DMA controller must use the format
described in the dma.txt file, using a two-cell specifier for each channel.

Example:

bcm2835_i2s: i2s@7e203000 {
	compatible = "brcm,bcm2835-i2s";
	reg = <	0x7e203000 0x20>,
	      < 0x7e101098 0x02>;

	dmas = <&dma 2>,
	       <&dma 3>;
	dma-names = "tx", "rx";
};