arm64: dts: renesas: r8a77965: Add Watchdog Timer controller node using RCLK Watchdog Timer

Add a device node for the Watchdog Timer (WDT) controller on the Renesas
R-Car M3-N (R8A77965) SoC.

Based on a similar patch of the R8A7796 device tree
by Geert Uytterhoeven <geert+renesas@glider.be>.
Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

arch/arm64/boot/dts/renesas/r8a77965.dtsi

@@ -139,8 +139,13 @@ soc {
 		ranges;
 
 		wdt0: watchdog@e6020000 {
+			compatible = "renesas,r8a77965-wdt",
+				     "renesas,rcar-gen3-wdt";
 			reg = <0 0xe6020000 0 0x0c>;
-			/* placeholder */
+			clocks = <&cpg CPG_MOD 402>;
+			power-domains = <&sysc R8A77965_PD_ALWAYS_ON>;
+			resets = <&cpg 402>;
+			status = "disabled";
 		};
 
 		gpio0: gpio@e6050000 {