dt-bindings: watchdog: renesas-wdt: Document r8a779f0 support

Document support for the Watchdog Timer (WDT) Controller in the Renesas
R-Car S4-8 (R8A779F0) SoC.

Signed-off-by: Thanh Quan <thanh.quan.xn@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/cca61a83ae82ecf5c23eb28e30c39f2f661f0e02.1642525158.git.geert+renesas@glider.be
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>