f2fs: support .shutdown in f2fs_sops

[ Upstream commit ee745e47 ]

Support .shutdown callback in f2fs_sops, then, it can be called to
shut down the file system when underlying block device is marked dead.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Stable-dep-of: c7f114d8 ("f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()")
Signed-off-by: Sasha Levin <sashal@kernel.org>