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>