Add support of Renesas R-Car Gen5 window watchdog timer. Timeout configuration is derived from CONFIG_WATCHDOG_TIMEOUT_MSECS, which is more accurate than the 1-second granularity 'timeout' passed to .start callback. Reviewed-by: Stefan Roese <stefan.roese@mailbox.org> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>