io_uring: serialize ctx->rings->sq_flags with atomic_or/and

Rather than require ctx->completion_lock for ensuring that we don't
clobber the flags, use the atomic bitop helpers instead. This removes
the need to grab the completion_lock, in preparation for needing to set
or clear sq_flags when we don't know the status of this lock.

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20220426014904.60384-3-axboe@kernel.dk


Signed-off-by: Jens Axboe <axboe@kernel.dk>