doc: dt: dma: add binding doc for pl08x

This introduces device tree bindings for the PL08x DMA controllers
when used with fixed signal assignment per channel, i.e. if each
channel on the PL08x is assigned precisely one burst/single signal
set.

[je: remove channel sub-node parsing, use cell value to assign AHB]
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NJoachim Eastwood <manabian@gmail.com>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

Documentation/devicetree/bindings/dma/arm-pl08x.txt

+* ARM PrimeCells PL080 and PL081 and derivatives DMA controller
+
+Required properties:
+- compatible: "arm,pl080", "arm,primecell";
+	      "arm,pl081", "arm,primecell";
+- reg: Address range of the PL08x registers
+- interrupt: The PL08x interrupt number
+- clocks: The clock running the IP core clock
+- clock-names: Must contain "apb_pclk"
+- lli-bus-interface-ahb1: if AHB master 1 is eligible for fetching LLIs
+- lli-bus-interface-ahb2: if AHB master 2 is eligible for fetching LLIs
+- mem-bus-interface-ahb1: if AHB master 1 is eligible for fetching memory contents
+- mem-bus-interface-ahb2: if AHB master 2 is eligible for fetching memory contents
+- #dma-cells: must be <2>. First cell should contain the DMA request,
+              second cell should contain either 1 or 2 depending on
+              which AHB master that is used.
+
+Optional properties:
+- dma-channels: contains the total number of DMA channels supported by the DMAC
+- dma-requests: contains the total number of DMA requests supported by the DMAC
+- memcpy-burst-size: the size of the bursts for memcpy: 1, 4, 8, 16, 32
+  64, 128 or 256 bytes are legal values
+- memcpy-bus-width: the bus width used for memcpy: 8, 16 or 32 are legal
+  values
+
+Clients
+Required properties:
+- dmas: List of DMA controller phandle, request channel and AHB master id
+- dma-names: Names of the aforementioned requested channels
+
+Example:
+
+dmac0: dma-controller@10130000 {
+	compatible = "arm,pl080", "arm,primecell";
+	reg = <0x10130000 0x1000>;
+	interrupt-parent = <&vica>;
+	interrupts = <15>;
+	clocks = <&hclkdma0>;
+	clock-names = "apb_pclk";
+	lli-bus-interface-ahb1;
+	lli-bus-interface-ahb2;
+	mem-bus-interface-ahb2;
+	memcpy-burst-size = <256>;
+	memcpy-bus-width = <32>;
+	#dma-cells = <2>;
+};
+
+device@40008000 {
+	...
+	dmas = <&dmac0 0 2
+		&dmac0 1 2>;
+	dma-names = "tx", "rx";
+	...
+};