io_uring/rsrc: use wq for quiescing

io_uring/rsrc: use wq for quiescing

Replace completions with waitqueues for rsrc data quiesce, the main
wakeup condition is when data refs hit zero. Note that data refs are
only changes under ->uring_lock, so we prepare before mutex_unlock()
reacquire it after taking the lock back. This change will be needed
in the next patch.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/1d0dbc74b3b4fd67c8f01819e680c5e0da252956.1681395792.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>