ide: merge ide_match_hwif() and ide_find_port()

* Change ide_match_hwif() argument from 'u8 bootable' to
  'struct ide_port_info *d'.

* Move ide_match_hwif() to ide-probe.c from setup-pci.c and rename
  it to ide_find_port_slot().  Update some comments while at it.

* ide_find_port() can be now just a wrapper for ide_find_port_slot().

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>