f2fs: give priority to select unpinned section for foreground GC

f2fs: give priority to select unpinned section for foreground GC

[ Upstream commit 71419129625a50cfb5e3c5cc215948a3f98c806d ]

Previously, during foreground GC, if victims contain data of pinned file,
it will fail migration of the data, and meanwhile i_gc_failures of that
pinned file may increase, and when it exceeds threshold, GC will unpin
the file, result in breaking pinfile's semantics.

In order to mitigate such condition, let's record and skip section which
has pinned file's data and give priority to select unpinned one.

Signed-off-by: Chao Yu <chao.yu@oppo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>