gpio: sysfs: fix chip removal with GPIOs exported over sysfs

gpio: sysfs: fix chip removal with GPIOs exported over sysfs

Currently if we export a GPIO over sysfs and unbind the parent GPIO
controller, the exported attribute will remain under /sys/class/gpio
because once we remove the parent device, we can no longer associate the
descriptor with it in gpiod_unexport() and never drop the final
reference.

Rework the teardown code: provide an unlocked variant of
gpiod_unexport() and remove all exported GPIOs with the sysfs_lock taken
before unregistering the parent device itself. This is done to prevent
any new exports happening before we unregister the device completely.

Cc: stable@vger.kernel.org
Fixes: 1cd53df733c2 ("gpio: sysfs: don't look up exported lines as class devices")
Link: https://patch.msgid.link/20260212133505.81516-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>