[SCSI] zfcp: provide support for NPIV

N_Port ID Virtualization (NPIV) allows a single FCP port to appear as
multiple, distinct ports providing separate port identification. NPIV
is supported by FC HBAs on System z9. zfcp was adapted to support this
new feature.

Signed-off-by: Andreas Herrmann <aherrman@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>