[IA64] Simple memory hot-add for ia64.

First step to memory hotplug for ia64 (add only,
all new memory is added to node 0, does not use
ZONE_EASY_RECLAIM yet).

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>