IMSM: Add support for VMD

IMSM: Add support for VMD

The Intel Volume Management Device (VMD) is an integrated
endpoint on the platform's PCIe root complex that acts
as a host bridge to a secondary PCIe domain.

This patch adds proper handling of NVMe devices attached to VMD domain.
Each VMD domain is treated as a separate controller (HBA).
Spanning between domains is forbidden.

Signed-off-by: Pawel Baldysiak <pawel.baldysiak@intel.com>
Signed-off-by: NeilBrown <neilb@suse.com>