dt-bindings: dmaengine: Introduce RZN1 dmamux bindings

dt-bindings: dmaengine: Introduce RZN1 dmamux bindings

The Renesas RZN1 DMA IP is based on a DW core, with eg. an additional
dmamux register located in the system control area which can take up to
32 requests (16 per DMA controller). Each DMA channel can be wired to
two different peripherals.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20220427095653.91804-2-miquel.raynal@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>