[SCSI] zfcp: non-experimental support for DIF/DIX

DIF/DIX support for zfcp is no longer experimental,
and config option is no longer necessary.
Return error from queuecommand for unsupported data directions.

Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>