Fix section mismatch of memory hotplug related code.

This is to fix many section mismatches of code related to memory hotplug.
I checked compile with memory hotplug on/off on ia64 and x86-64 box.

Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/mm/discontig.c

@@ -693,6 +693,7 @@ void __init paging_init(void)
 	zero_page_memmap_ptr = virt_to_page(ia64_imva(empty_zero_page));
 }
 
+#ifdef CONFIG_MEMORY_HOTPLUG
 pg_data_t *arch_alloc_nodedata(int nid)
 {
 	unsigned long size = compute_pernodesize(nid);
@@ -710,3 +711,4 @@ void arch_refresh_nodedata(int update_node, pg_data_t *update_pgdat)
 	pgdat_list[update_node] = update_pgdat;
 	scatter_node_data();
 }
+#endif