ide: add ->port_init_devs method to ide_hwif_t

* Add ->port_init_devs method to ide_hwif_t for a host specific
  initialization of devices on a port.  Call the new method from
  ide_port_init_devices().

* Convert ht6560b, qd65xx and opti621 host drivers to use the new
  ->port_init_devs method.

There should be no functionality changes caused by this patch.

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