s390/pci: Expose new port attribute for PCIe functions

s390/pci: Expose new port attribute for PCIe functions

BugLink: https://bugs.launchpad.net/bugs/1874056
Add SysFS attribute that provides the port number for PCI functions
representing a single port of a multi-port device.

Signed-off-by: Alexander Schmidt <alexs@linux.ibm.com>
Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
(backported from commit e6ab7490ffaed83d6581f512e66c7c8cc6f58c2d)
Signed-off-by: Frank Heimes <frank.heimes@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>