dt-bindings: dma: snps,dw-axi-dmac: Add fallback compatible for CV1800B

The previous version of the binding change only add compatible
string without adding the fallback compatible, this breaks
backward compatibility. Add the needed fallback compatible to
fix this.

Fixes: be3e2a0419c6 ("dt-bindings: dma: snps,dw-axi-dmac: Add CV1800B compatible")
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260511063818.463877-2-inochiama@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>