ARM: dts: r8a7744: Add RWDT node

Add a device node for the Watchdog Timer (RWDT) controller on the Renesas
RZ/G1N (r8a7744) SoC.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>