gpio: mockup: remove gpio debugfs when remove device

[ Upstream commit 303e6da9 ]

GPIO mockup debugfs is created in gpio_mockup_probe() but
forgot to remove when remove device. This patch add a devm
managed callback for removing them.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Sasha Levin <sashal@kernel.org>