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

In the Linux kernel, the following vulnerability has been resolved: 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.