gpio: sim: lock up configfs that an instantiated device depends on

gpio: sim: lock up configfs that an instantiated device depends on

Once a sim device is instantiated and actively used, allowing rmdir for
its configfs serves no purpose and can be confusing. Effectively,
arbitrary users start depending on its existence.

Make the subsystem itself depend on the configfs entry for a sim device
while it is in active use.

Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Link: https://lore.kernel.org/r/20250103141829.430662-5-koichiro.den@canonical.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>