watchdog: rt2880-wdt: avoid static global declarations

Instead of using static global definitions in driver code, refactor code
introducing a new watchdog driver data structure and use it along the code.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230301065510.2818425-1-sergio.paracuellos@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>