nvme: move timeout variables to core.c

nvme: move timeout variables to core.c

These variables are used by PCI driver and will also be used in the
forthcoming NVMe over Fabrics drivers.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit ba0ba7d3e5266111ec865b0bf1ad48dd0e2a2314)

Orabug: 25130845

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