[SCSI] libfc: add some generic NPIV support routines to libfc

Adds a function to create a new VN_Port instances, which share the EM
list with the N_Port, VN_Port lookup by fabric ID when responding to a new
request (otherwise the exchange lookup from the N_Ports EM list is trusted to
return an exchange with a cached lport value for the correct VN_Port),
a pointer to a fc_vport structure for VN_Ports, and flags to indicate if an
N_Port supports NPIV and if the switch/fabric allows it.

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: Robert Love <robert.w.love@intel.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>