f2fs: move ext_lock out of struct extent_info

Move ext_lock out of struct extent_info, then in the following patches we can
use variables with struct extent_info type as a parameter to pass pure data.

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
4 files changed