dt-bindings: dmaengine: Add dma multiplexer for CV18XX/SG200X series SoC

dt-bindings: dmaengine: Add dma multiplexer for CV18XX/SG200X series SoC

The DMA IP of Sophgo CV18XX/SG200X is based on a DW AXI CORE, with
an additional channel remap register located in the top system control
area. The DMA channel is exclusive to each core.

In addition, the DMA multiplexer is a subdevice of system controller,
so this binding only contains necessary properties for the multiplexer
itself.

Add the dmamux binding for CV18XX/SG200X series SoC.

Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250611081000.1187374-2-inochiama@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>