f2fs: split need_inplace_update

This patch splits need_inplace_update to two functions:
a. should_update_inplace() includes all conditions that we must use IPU.
b. should_update_outplace() includes all conditions that we must use OPU.

So that, in f2fs_ioc_set_pin_file() and f2fs_defragment_range(), we can
use corresponding function to check whether we can trigger OPU/IPU or not.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>