From Andries.Brouwer@cwi.nl.

- kill redundant, never executed code in lba_capacity_is_ok()
- add idedisk_supports_{hpa,lba48}() helpers
- don't recalculate drive->cyl for drives using LBA addressing,
  we never fall-back to CHS, so its useless and confusing
- remove wrong drive->head and drive->sect assignments for LBA-48
- don't overwrite id->lba_capacity and id->lba_capacity_2