BACKPORT: loop: Factor out configuring loop from status

Factor out this code into a separate function, so it can be reused by
other code more easily.

Signed-off-by: Martijn Coenen <maco@android.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 0c3796c244598122a5d59d56f30d19390096817f)
Bug: 148607611
Change-Id: I58343d283b38da77d14d9cb61003947021ba5633