arm64: dts: renesas: spider-cpu: Enable watchdog timer

Enable the watchdog timer on the Spider board.

Extracted from a larger patch in the BSP by LUU HOAI.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NGuenter Roeck <linux@roeck-us.net>
Reviewed-by: NWolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/b36b2bb5770e10d906571721a3d73ca205b6f56e.1642525158.git.geert+renesas@glider.be

arch/arm64/boot/dts/renesas/r8a779f0-spider-cpu.dtsi

@@ -31,6 +31,11 @@
 	clock-frequency = <32768>;
 };
 
+&rwdt {
+	timeout-sec = <60>;
+	status = "okay";
+};
+
 &scif3 {
 	status = "okay";
 };