arm64: dts: renesas: r8a774b1: Add DU device to DT

Add the DU device to r8a774b1 SoC DT.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/1570029619-43238-3-git-send-email-biju.das@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>