gpio: mockup: remove gpio debugfs when remove device

stable inclusion
from stable-v5.10.144
commit 3815e66c2183f3430490e450ba16779cf5214ec6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6D0V7

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3815e66c2183f3430490e450ba16779cf5214ec6



--------------------------------

[ 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>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>
Reviewed-by: Zheng Zengkai <zhengzengkai@huawei.com>