[SCSI] libfc: changes to libfc_host_alloc to consolidate initialization with allocation

I'd like to keep basic initialization together with allocation, which means
this can't just be a tail-call to scsi_host_alloc.

This is needed to create a generic libfc host allocation routine for NPIV
VN_Ports, which will share the exchange ID space (through sharing exchange
manager structures) with the parent lport.  In order to clone the exchange
manager list when the lport is allocated, the list head must be initialized
earlier.

Also, update fnic to use the libfc_host_alloc so that later changes do not break
it. (contribution by Joe Eykholt)

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