dmaengine: sun6i: Add driver for the Allwinner A31 DMA controller
The Allwinner A31 has a 16 channels DMA controller that it shares with the
newer A23. Although sharing some similarities with the DMA controller of the
older Allwinner SoCs, it's significantly different, I don't expect it to be
possible to share the driver for these two.
The A31 Controller is able to memory-to-memory or memory-to-device transfers on
the 16 channels in parallel.