f2fs: show flush list status in sysfs

This patch adds to show flush list status in sysfs.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 461e22d..3961cea 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -2702,7 +2702,8 @@
 	int free_nids, avail_nids, alloc_nids;
 	int total_count, utilization;
 	int bg_gc, nr_wb_cp_data, nr_wb_data;
-	int nr_flushing, nr_flushed, nr_discarding, nr_discarded;
+	int nr_flushing, nr_flushed, flush_list_empty;
+	int nr_discarding, nr_discarded;
 	int nr_discard_cmd;
 	unsigned int undiscard_blks;
 	int inline_xattr, inline_inode, inline_dir, append, update, orphans;