This patch adds the following new files:

  include/scsi/scsi_cmnd.h
  include/scsi/scsi_device.h
  include/scsi/scsi_host.h

for each of the major scsi core data structures and makes the
old scsi.h and hosts.h include them for compatibality.  In the
next round of patches all reamining contents of those will
move to proper locations.