MIPS: dts: jz4780: Add DMA controller node to the devicetree

Add the devicetree node to support the DMA controller found
in JZ480 SoCs.

Tested-by: Mathieu Malaterre <malat@debian.org>
Acked-by: James Hogan <jhogan@kernel.org>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.co.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>