support for per driver parameters added in lk 2.5.31

1.62 changes:
  - driverfs support for these options (more to come):
    /driverfs/bus/scsi/drivers/scsi_debug/delay [rw]
    /driverfs/bus/scsi/drivers/scsi_debug/num_devs [r]
    /driverfs/bus/scsi/drivers/scsi_debug/opts [rw]
  - start using some C99
  - fdisk requires EINVAL from unsupported ioctls
    (scsi_debug previously used ENOTTY)

1.61 changes:
  - simulate delayed responses, controlled by
    'scsi_debug_delay'
  - support REPORT LUNS
  - support more MODE SENSE pages
  - [following Doug Ledford's suggestion] do autosense
    (i.e. set Scsi_Cmnd::sense_buffer array appropriately
     when a status of CHECK CONDITION is set)
  - minor driverfs support
  - start adding error injection logic, see
    "scsi_debug_every_nth"

Doug Gilbert