Add a binding for A100's dma controller.

Signed-off-by: Yangtao Li <frank@allwinnertech.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/f15a18e9b8868e8853db1b5a3d1e411b0ac1c63a.1604988979.git.frank@allwinnertech.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>