4 Patch summary of PCIe re-arrangement of nvme code for future technology expansion

[J Freyensee]

The four patch series following this email is based on a previous email
thread and the following suggestion:

 a) move files to a new directory.
 b) start splitting struct nvme_dev into a generic struct nvme_ctrl
    and a PCI-specific nvme_pci_ctrl

The goal is still based on the previous patch submission (subject "Move
nvme driver source into subdirectory and move pci specifics from core
into separate file") which:

 - moved files to a new directory
 - split data structures
 - split files
 - introduced a new internal API

to enable future technology expansion of the NVMe protocol.