arm64: dts: renesas: white-hawk-cpu: Enable watchdog timer

Enable the watchdog timer on the White Hawk CPU board.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/77a0e29d965032115de1f07ceecb2d5d07db74eb.1662715538.git.geert+renesas@glider.be