nvme: move ns id info to struct nvme_ns_head

Move the namesapce info to struct nvme_ns_head, because it's the same
for all associated namespaces.

Note: with multipathing enabled the PI information is shared between all
paths. If a path is using a different PI configuration it will overwrite
the previous settings. This is obviously not correct and such
configuration will be rejected in future. For the time being we expect
a correctly configured storage.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>