[SCSI] fcoe: fcoe_interface create, destroy and refcounting

Up to this point the fcoe_instance structure was simply kzalloc/kfreed.  This
patch introduces create and destroy functions as well as kref based reference
counting.  The create function will grow as the initialization code is moved
there.

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>