watchdog: designware: Optionally fetch clock and reset from DT

Add optional support for fetching watchdog clock rate from DT
and ungating reset via reset framework. This is optional as not
all platforms using DW WDT support the clock and reset frameworks
yet.

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>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # roc-rk3399-pc