No platform-device is required for IO(x)APICs, so don't even
create them.

[ rjw: This fixes a problem with leaking platform device objects
  after IOAPIC/IOxAPIC hot-removal events.]
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>