ide: add ide_ports[]

* Add ide_ports[] table keeping pointers to all initialized ports.

* Set ide_ports[] entry for a given port in init_irq() and clear it
  ide_remove_port_from_hwgroup().

* Convert init_irq() to use ide_ports[] instead of ide_hwifs[] for
  grouping ports into hwgroup.

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