tighen and expand error handling, mostly for NCQ use cases:
- make retry timeout callout per xfer, i.e. retry separately
- zero whole bio struct on retry to avoid more stale state
- add a REQUEUE option, which doesn't bump retry count
- add ata_read_log_ext_ncq() for NCQ recovery
- adjust logic for activating xfers - allow next command only when
  it's for same drive, several concurrent are only supported when HBA
  and driver support FIS-based switching
- add new ata_timeout() which handles race between callout_stop()
  and the invokation, add appropriate handling on deactivate/free paths
- stop using ch_status/ch_error in non-wdc code; later it will be dropped
  completely

(jdolecek)