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

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.

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