[SCSI] zfcp: Move sbale handling to zfcp_qdio files

Move the code accessing the qdio sbales and zfcp_qdio_req struct to
the zfcp_qdio files and provide helper functions for accessing the
qdio related parts.

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>