nvme: move namespace scanning to common code

nvme: move namespace scanning to common code

The namespace scanning code has been mostly generic already, we just
need to store a pointer to the tagset in the nvme_ctrl structure, and
add a method to check if a controller is I/O incapable.  The latter
will hopefully be replaced by a proper controller state machine soon.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[Fixed pr conflicts]
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 5bae7f73d378a986671a3cad717c721b38f80d9e)

Orabug: 25130845
Conflicts:
    drivers/nvme/host/nvme.h
    drivers/nvme/host/pci.c

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