ide: allocate ide_hwif_t instances dynamically

* Allocate ide_hwif_t instances dynamically and remove ide_hwifs[].

  This cuts almost ~14kB from ide-probe.o (x86-32, MAX_HWIFS == 10):

   text    data     bss     dec     hex filename
   9140      40   14084   23264    5ae0 drivers/ide/ide-probe.o.before
   9169      40      44    9253    2425 drivers/ide/ide-probe.o.after

* Remove no longer needed ide_init_port_data() call from ide_unregister().

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