dt-bindings: watchdog: renesas-wdt: Document r8a774a1 support

RZ/G2M (R8A774A1) watchdog implementation is compatible with R-Car
Gen3, therefore add relevant documentation.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
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

@@ -7,6 +7,7 @@ Required properties:
 	       Examples with soctypes are:
 		 - "renesas,r8a7743-wdt" (RZ/G1M)
 		 - "renesas,r8a7745-wdt" (RZ/G1E)
+		 - "renesas,r8a774a1-wdt" (RZ/G2M)
 	         - "renesas,r8a7790-wdt" (R-Car H2)
 	         - "renesas,r8a7791-wdt" (R-Car M2-W)
 	         - "renesas,r8a7792-wdt" (R-Car V2H)
@@ -21,8 +22,8 @@ Required properties:
 	         - "renesas,r7s72100-wdt" (RZ/A1)
 		The generic compatible string must be:
 		 - "renesas,rza-wdt" for RZ/A
-		 - "renesas,rcar-gen2-wdt" for R-Car Gen2 and RZ/G
-		 - "renesas,rcar-gen3-wdt" for R-Car Gen3
+		 - "renesas,rcar-gen2-wdt" for R-Car Gen2 and RZ/G1
+		 - "renesas,rcar-gen3-wdt" for R-Car Gen3 and RZ/G2
 
 - reg : Should contain WDT registers location and length
 - clocks : the clock feeding the watchdog timer.