f2fs: move grabing orphan pages out of protection region

Move grabing orphan block page out of protection region, and grab all
the orphan block pages ahead.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
[Jaegeuk Kim: remove unnecessary code pointed by Chao Yu]
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>