Add DECLARE_ICH_DEV() macro.

While at it:

* Add init_hwif_ich() (->init_hwif method) for ICH controllers.

* Rename init_chipset_piix() to init_chipset_ich() and use it only for
  ICH controllers.

* Remove no longer needed piix_is_ichx() helper.
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>