NVMe: Allow user initiated rescan

NVMe: Allow user initiated rescan

This exposes ioctl and sysfs methods a user can invoke to request the
driver rescan a controller and its namespaces. This is less harsh than
doing a controller reset, which temporarilly halts all IO, just to
surface a newly attached namespace.

This is mainly useful for controllers that implement the namespace
management command, but do not support the namespace notify change
asynchronous event notification.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 9ec3bb2f994bda9c8817856fdcbfaebe8f62fbd3)

Orabug: 25130845

Signed-off-by: Ashok Vairavan <ashok.vairavan@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>