dt-bindings: watchdog: renesas-wdt: Add support for the r8a77995 wdt

Document support for the Watchdog Timer (WDT) Controller in the Renesas
R-Car D3 (r8a77995) SoC.

No driver update is needed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>