ide: add ide_proc_register_port()

* create_proc_ide_interfaces() tries to add /proc entries for every probed
  and initialized IDE port, replace it by ide_proc_register_port() which does
  it only for the given port (also rename destroy_proc_ide_interface() to
  ide_proc_unregister_port() for consistency)
  
* convert {create,destroy}_proc_ide_interface[s]() users to use new functions

* pmac driver depended on proc_ide_create() to add /proc port entries, fix it
  
* au1xxx-ide, swarm and cs5520 drivers depended indirectly on ide-generic
  driver (CONFIG_IDE_GENERIC=y) to add port /proc entries, fix them

* there is now no need to add /proc entries for IDE ports in proc_ide_create()
  so don't do it

* proc_ide_create() needs now to be called before drivers are probed - fix it,
  while at it make proc_ide_create() create /proc "ide" directory

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