[SCSI] zfcp: Simplify handling of ct and els requests

Remove some redundancies in FC related code and trace:
- drop redundant data from SAN trace (local s_id that only changes
  during link down, ls_code that is already part of payload, d_id in
  ct response trace that is always the same as in ct request trace)
- use one common fsf struct to hold zfcp data for ct and els requests
- leverage common fsf struct for FC passthrough job data, allocate it
  with dd_bsg_data for passthrough requests and unify common code for
  ct and els passthrough request
- simplify callback handling in zfcp_fc

Reviewed-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>