- Replace the task_io_reg_t with the simple u8. There is no need to obfuscate
   the code more then necessary.

- kill some unnecessary type definitions out from hdreg.h.

- Add proper attributes to register files in hdreg.h.

- Don't use raw arrays for tfRegister and hobRegister in ide_task_s.  Use out
   nice global structures describing the fields in them.  This allows to kill
   the following defines:

     IDE_DATA_OFFSET
     IDE_FEATURE_OFFSET
     IDE_NSECTOR_OFFSET
     IDE_SECTOR_OFFSET
     IDE_LCYL_OFFSET
     IDE_HCYL_OFFSET
     IDE_SELECT_OFFSET
     IDE_COMMAND_OFFSET

   and many many others.

- Please have a look at the following in pdc4030.c. It couldn't have worked!
   This has been fixed in one go with the above change:

   memcpy(args.hobRegister, NULL, sizeof(struct hd_drive_hob_hdr));

- Kill the redundant *_REG_HOB definitions. They don't help readability in any
   way.