[IA64] Make PCI Express support selectable

When I tried to use PCI Express Hotplug driver on my ia64 box, I
noticed that "PCI Express support" is not even selectable on ia64.
This patch makes PCI Express support selectable.

Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>