dt-bindings: dma: rz-dmac: Document RZ/G2UL SoC

Document RZ/G2UL DMAC bindings. RZ/G2UL DMAC is identical to one found
on the RZ/G2L SoC. No driver changes are required as generic compatible
string "renesas,rz-dmac" will be used as a fallback.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220206200308.14315-1-biju.das.jz@bp.renesas.com


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