[IA64] Fix simscsi for new SCSI midlayer

The sd driver now uses scsi_execute_req() for almost everything.
scsi_execute_req() converts requests into scatterlists.

Fix the HP SCSI disk simulator to understand scatterlists for
more commands.

Without this patch the current kernel will not boot on the simulator
(the disks are always detected as having no sectors, and so cannot be
mounted).

Signed-off-by: Peter Chubb <peterc@gelato.unsw.edu.au>
Signed-off-by: Tony Luck <tony.luck@intel.com>