nvme: limit visible namespaces on Apple S3X

[guest-seuros]

Summary

The Apple S3X controller exposes internal namespaces beyond NSID 1
that aren't meant to be visible to the OS. Added QUIRK_APPLE_S3X_NS1_ONLY
and nvme_ctrlr_num_namespaces()/nvme_ctrlr_nsid_visible() helpers, and
route namespace construction, notification, and AER namespace-changed
handling through them instead of a raw cdata.nn count.

MFC after: 1 week

[imp]

This looks good.
Sometimes I might have split the new quirk from the new behavior, but this case seems to be fine because (a) splitting it wouldn't help bisectability and (b) splitting wouldn't make it easier to review.

[guest-seuros]

I hope to get this code removed once we have MQS.

Disk Speed is ok, but it has the capability to be faster.