watchdog: wm831x_wdt: Remove GPIO handling

An attempt to convert the driver to using GPIO descriptors
(see Link tag) was discouraged in favor of deleting the
handling of the update GPIO altogehter since there are
no in-tree users.

This patch deletes the GPIO handling instead.

Cc: Richard Fitzgerald <rf@opensource.cirrus.com>
Cc: Charles Keepax <ckeepax@opensource.cirrus.com>
Cc: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/linux-watchdog/20200210102209.289379-1-linus.walleij@linaro.org/


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20200229115046.57781-1-linus.walleij@linaro.org


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