arm64: dts: renesas: r8a774c0: Add SYS-DMAC controller nodes

Add sys-dmac[012] device nodes for the RZ/G2E SoC (a.k.a. r8a774c0).

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>