nvme-fabrics: Add FC transport LLDD api definitions

Host:
 - LLDD registration with the host transport
 - registering host ports (local ports) and target ports seen on
   fabric (remote ports)
 - Data structures and call points for FC-4 LS's and FCP IO requests

Target:
 - LLDD registration with the target transport
 - registering nvme subsystem ports (target ports)
 - Data structures and call points for reception of FC-4 LS's and
   FCP IO requests, and callbacks to perform data and rsp transfers
   for the io.

Add to MAINTAINERS file

Signed-off-by: James Smart <james.smart@broadcom.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jay Freyensee <james_p_freyensee@linux.intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>