dt-bindings: watchdog: renesas,wdt: Document r8a7742 support

RZ/G1H (R8A7742) watchdog implementation is compatible with R-Car Gen2,
therefore add relevant documentation.
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml

@@ -24,6 +24,7 @@ properties:
 
       - items:
           - enum:
+              - renesas,r8a7742-wdt      # RZ/G1H
               - renesas,r8a7743-wdt      # RZ/G1M
               - renesas,r8a7744-wdt      # RZ/G1N
               - renesas,r8a7745-wdt      # RZ/G1E