Continuation of descriptor sense data expansion to
sg driver.

Next will be the sd driver which awaits a
new utility function in constants.c to read the
sense data information field for medium/hardware
errors.

Changelog:
   - expand sense data handling to descriptor format
   - make module parameters visible in
       /sys/modules/sg/parameters
   - add "readable" SCSI commands: READ(16), REPORT LUNS,
     SERVICE_ACTION_IN, RECEIVE_DIAGNOSTIC, READ_LONG
     and MAINTENANCE_IN_CMD to list

Signed-off-by: Douglas Gilbert <dougg@torque.net>