scsi: create common SCSIRequest structure. Rename the SCSIRequest structs in scsi-disk.c and scsi-generic.c to SCSIDiskReq and SCSIGenericReq. Create a SCSIRequest struct and move the common elements over. Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>