dt-bindings: dma: renesas,usb-dmac: add r8a77961 support

This patch adds support for r8a77961 (R-Car M3-W+).

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/1585117138-8408-1-git-send-email-yoshihiro.shimoda.uh@renesas.com


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