[SCSI] isci: enable wide port targets

Arrange for task_contexts prepared for the wide targets to account for
all the attached phys in the port.

Signed-off-by: Bartek Nowakowski <bartek.nowakowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>