f2fs: use attach/detach_page_private

Since the new pair function is introduced, we can call them to clean the
code in f2fs.h.

Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Chao Yu <yuchao0@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Link: http://lkml.kernel.org/r/20200517214718.468-6-guoqing.jiang@cloud.ionos.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>