dt-bindings: dma: add schema for altera-msgdma

add yaml schema for Altera mSGDMA bindings in devicetree.

Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olivier Dautricourt <olivier.dautricourt@orolia.com>
Link: https://lore.kernel.org/r/7487a25cdb240d1be4a8593aa602c3c73d8f5acb.1623251990.git.olivier.dautricourt@orolia.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>