nvme: store a struct device pointer in struct nvme_dev

nvme: store a struct device pointer in struct nvme_dev

Most users want the generic device, so store that in struct nvme_dev
instead of the pci_dev.  This also happens to be a nice step towards
making some code reusable for non-PCI transports.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit e75ec752d725b7b612c0b2db1bca50a9e53c0879)

Orabug: 22620486
Signed-off-by: Jason Luo <zhangqing.luo@oracle.com>
Conflicts:
	drivers/block/nvme-core.c