ppc/pmac: remove ppc_ide_md hooks

* Add pmac_ide_init_ports() helper and use it instead of
  pmac_ide_init_hwif_ports().

* Remove ppc_ide_md hooks - no need for them
  (IDE pmac host driver takes care of all this setup).

* Then remove no longer needed <linux/ide.h> include
  from arch/powerpc/platforms/powermac/pmac.h.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>