watchdog: designware: Migrate CONFIG_DESIGNWARE_WATCHDOG to Kconfig

Migrate CONFIG_DESIGNWARE_WATCHDOG to Kconfig and update the headers
accordingly, no functional change. The S10 enables the WDT only in
SPL, but does not enable it in U-Boot itself, hence disable it in
the config again.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dalon Westergreen <dwesterg@gmail.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>
Cc: Philipp Tomisch <philipp.tomisch@theobroma-systems.com>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tien Fong Chee <tien.fong.chee@intel.com>