Fix build error for numa_clear_node() under IA64

numa_clear_node() function is not implemented under IA64,
it will be called in unmap_cpu_on_node() in mm/memory_hotplug.c.
This cause build error under IA64, this patch adds numa_clear_node()
in IA64 to fix this problem.

[Added __cpuinit notation to numa_clear_node() to keep linker happy -Tony]

Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>