DT: dmaengine: rcar-dmac: document R8A7743/5 support

Renesas  RZ/G SoC also have the R-Car gen2/3 compatible DMA controllers.
Document RZ/G1[ME] (also known as R8A774[35]) SoC bindings.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>