[SCSI] zfcp: Add zfcp private struct as SCSI device driver data

Add a new data structure zfcp_scsi_dev that holds zfcp private data
for each SCSI device. Use scsi_transport_reserve_device to let the
SCSI midlayer automatically allocate this with each SCSI device.

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>