dt-bindings: dma: Add binding for jz4780-dma

Add device tree bindings for the DMA controller on JZ4780 SoCs, used by
the dma-jz4780 driver.
Signed-off-by: Alex Smith <alex.smith@imgtec.com>
Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Documentation/devicetree/bindings/dma/jz4780-dma.txt

+* Ingenic JZ4780 DMA Controller
+
+Required properties:
+
+- compatible: Should be "ingenic,jz4780-dma"
+- reg: Should contain the DMA controller registers location and length.
+- interrupts: Should contain the interrupt specifier of the DMA controller.
+- interrupt-parent: Should be the phandle of the interrupt controller that
+- clocks: Should contain a clock specifier for the JZ4780 PDMA clock.
+- #dma-cells: Must be <2>. Number of integer cells in the dmas property of
+  DMA clients (see below).
+
+Optional properties:
+
+- ingenic,reserved-channels: Bitmask of channels to reserve for devices that
+  need a specific channel. These channels will only be assigned when explicitly
+  requested by a client. The primary use for this is channels 0 and 1, which
+  can be configured to have special behaviour for NAND/BCH when using
+  programmable firmware.
+
+Example:
+
+dma: dma@13420000 {
+	compatible = "ingenic,jz4780-dma";
+	reg = <0x13420000 0x10000>;
+
+	interrupt-parent = <&intc>;
+	interrupts = <10>;
+
+	clocks = <&cgu JZ4780_CLK_PDMA>;
+
+	#dma-cells = <2>;
+
+	ingenic,reserved-channels = <0x3>;
+};
+
+DMA clients must use the format described in dma.txt, giving a phandle to the
+DMA controller plus the following 2 integer cells:
+
+1. Request type: The DMA request type for transfers to/from the device on
+   the allocated channel, as defined in the SoC documentation.
+
+2. Channel: If set to 0xffffffff, any available channel will be allocated for
+   the client. Otherwise, the exact channel specified will be used. The channel
+   should be reserved on the DMA controller using the ingenic,reserved-channels
+   property.
+
+Example:
+
+uart0: serial@10030000 {
+	...
+	dmas = <&dma 0x14 0xffffffff
+		&dma 0x15 0xffffffff>;
+	dma-names = "tx", "rx";
+	...
+};