ARM: dts: r9a06g032: Describe the DMA router

There is a dmamux on this SoC which allows picking two different sources
for a single DMA request.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20220427095653.91804-10-miquel.raynal@bootlin.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>