watchdog: make nowayout sysfs file writable

It can be useful to delay setting the nowayout feature for a watchdog
device. Moreover, not every driver (notably gpio_wdt) implements a
nowayout module parameter/otherwise respects CONFIG_WATCHDOG_NOWAYOUT,
and modifying those drivers carries a risk of causing a regression for
someone who has two watchdog devices, sets CONFIG_WATCHDOG_NOWAYOUT
and somehow relies on the gpio_wdt driver being ignorant of
that (i.e., allowing one to gracefully close a gpio_wdt but not the
other watchdog in the system).

So instead, simply make the nowayout sysfs file writable. Obviously,
setting nowayout is a one-way street.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191105205118.11359-1-linux@rasmusvillemoes.dk


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