arm64: dts: renesas: r8a774b1: Add RWDT node

Populate the device tree node for the Watchdog Timer (RWDT)
controller on the Renesas RZ/G2N (r8a774b1) SoC.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Link: https://lore.kernel.org/r/1570178133-21532-5-git-send-email-fabrizio.castro@bp.renesas.com


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