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

arch/arm64/boot/dts/renesas/r8a774b1.dtsi

@@ -151,8 +151,13 @@ soc {
 		ranges;
 
 		rwdt: watchdog@e6020000 {
+			compatible = "renesas,r8a774b1-wdt",
+				     "renesas,rcar-gen3-wdt";
 			reg = <0 0xe6020000 0 0x0c>;
-			/* placeholder */
+			clocks = <&cpg CPG_MOD 402>;
+			power-domains = <&sysc R8A774B1_PD_ALWAYS_ON>;
+			resets = <&cpg 402>;
+			status = "disabled";
 		};
 
 		gpio0: gpio@e6050000 {