arm64: dts: renesas: r8a774b1: Add Sound and Audio DMAC device nodes

Based on a similar patch of the R8A7796 device tree
by Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Link: https://lore.kernel.org/r/1570200761-884-2-git-send-email-biju.das@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>