selftests: ublk: add one dependency header

Add one dependency helper which can include new uapi definition which
isn't synced from kernel.

This way also helps a lot for downstream test deployment.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250320013743.4167489-2-ming.lei@redhat.com


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