dt-bindings: watchdog: renesas-wdt: Document r8a77470 support

RZ/G1C (R8A77470) watchdog implementation is compatible with R-Car
Gen2, therefore add relevant documentation.
Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/devicetree/bindings/watchdog/renesas-wdt.txt

@@ -8,6 +8,7 @@ Required properties:
 		 - "renesas,r8a7743-wdt" (RZ/G1M)
 		 - "renesas,r8a7744-wdt" (RZ/G1N)
 		 - "renesas,r8a7745-wdt" (RZ/G1E)
+		 - "renesas,r8a77470-wdt" (RZ/G1C)
 		 - "renesas,r8a774a1-wdt" (RZ/G2M)
 		 - "renesas,r8a774c0-wdt" (RZ/G2E)
 	         - "renesas,r8a7790-wdt" (R-Car H2)