ahci - Reduce livelock warnings with ahci

ahci - Reduce livelock warnings with ahci

* Mark the ahci (sata) interrupt as HIFREQ to avoid triggering
  livelock warnings.

* Very high interrupt rates are possible with modern SSDs.  We
  don't use the AHCI chipset's interrupt rate moderation features
  because they are a bit problematic (often implemented via an
  unconditional delay even for single commands, for example).

  By flagging the interrupt as HIFREQ, the livelock code will
  trigger at kern.livelock_limit_hi instead of kern.livelock_limit.