watchdog: remove pnx83xx driver

Commit 625326ea ("MIPS: Remove PNX833x alias NXP_STB22x") removed
support for PNX833x, so it's time to remove watchdog driver, too.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201106130508.103598-1-tsbogend@alpha.franken.de


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