PCI: Add PCI_VDEVICE_SUB helper macro

PCI_VDEVICE_SUB generates the pci_device_id struct layout for
the specific PCI device/subdevice. Private data may follow the
output.

Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Piotr Kwapulinski <piotr.kwapulinski@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>