[SCSI] zfcp: Improve request allocation through mempools

Remove the special case for NO_QTCB requests and optimize the
mempool and cache processing for fsfreqs. Especially use seperate
mempools for the zfcp_fsf_req and zfcp_qtcb structs.

Signed-off-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>