scsi: be2iscsi: Add warning message for unsupported adapter

Add a warning message to indicate obsolete/unsupported
BE2 Adapter Family devices

Signed-off-by: Ketan Mukadam <ketan.mukadam@avagotech.com>
Signed-off-by: Jitendra Bhivare <jitendra.bhivare@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>