Don't override the cable type if the "idex=ata66" parameter was used.

While at it:

* atiixp.c: factor out cable detection to atiixp_cable_detect() from
  init_hwif_atiixp().

* cs5535.c: pass 'ide_hwif_t *hwif' instead of 'struct pci_dev *dev' to
  cs5535_cable_detect().

* scc_pata.c: factor out cable detection to scc_cable_detect() from
  init_hwif_scc() and remove incorrect comment.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>