[SCSI] zfcp: Use common code definitions for FC ELS structs

Use common code definitions for FC plogi, logo, rscn and adisc structs
instead of inventing private ones. Move the private struct for issuing
ELS ADISC inside zfcp to zfcp_fc header file.

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>