[SCSI] zfcp: Small QDIO cleanups

QBUFF_PER_PAGE is only used inside the qdio module, so move it to
zfcp_qdio.c

zfcp_qdio_zero_sbals is now only used in the qdio module, so make it
static.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>