ide: add ide_pci_remove() helper

* Add 'unsigned long host_flags' field to struct ide_host.

* Set ->host_flags in ide_host_alloc_all().

* Always set PCI dev's ->driver_data in ide_pci_init_{one,two}().

* Add ide_pci_remove() helper (the default implementation for
  struct pci_driver's ->remove method).

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