dmaengine: milbeaut-xdmac: Add XDMAC driver for Milbeaut platforms

Driver for Socionext Milbeaut XDMAC controller. The controller only
supports Mem-To-Mem transfers over upto 8 configurable channels.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Link: https://lore.kernel.org/r/20191015033219.14713-1-jassisinghbrar@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>