dmaengine: milbeaut-hdmac: Add HDMAC driver for Milbeaut platforms

Driver for Socionext Milbeaut HDMAC controller. The controller has
upto 8 floating channels, that need a predefined slave-id to work
from a set of slaves.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Link: https://lore.kernel.org/r/20191015033359.14925-1-jassisinghbrar@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>