ide: add ide_deprecated_find_port() helper

* Factor out code for finding ide_hwifs[] slot from ide_register_hw()
  to ide_deprecated_find_port().

* Convert bast-ide, ide-cs and delkin_cb host drivers to use ide_device_add()
  instead of ide_register_hw() (while at it drop doing "ide_unregister()" loop
  which tries to unregister _all_ IDE interfaces if useable ide_hwifs[] slot
  cannot be find).

This patch leaves us with only two ide_register_hw() users:
- drivers/macintosh/mediabay.c
- drivers/ide/ide.c

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