x86/mm/hotplug: Put kernel_physical_mapping_remove() declaration in CONFIG_MEMORY_HOTREMOVE

kernel_physical_mapping_remove() is only called by
arch_remove_memory() in init_64.c, which is enclosed in
CONFIG_MEMORY_HOTREMOVE. So when we don't configure
CONFIG_MEMORY_HOTREMOVE, the compiler will give a warning:

	warning: ‘kernel_physical_mapping_remove’ defined but not used

So put kernel_physical_mapping_remove() in
CONFIG_MEMORY_HOTREMOVE.
Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
Cc: linux-mm@kvack.org
Cc: gregkh@linuxfoundation.org
Cc: yinghai@kernel.org
Cc: wency@cn.fujitsu.com
Cc: mgorman@suse.de
Cc: tj@kernel.org
Cc: liwanp@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1366019207-27818-3-git-send-email-tangchen@cn.fujitsu.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/init_64.c

@@ -1019,6 +1019,7 @@ void __ref vmemmap_free(struct page *memmap, unsigned long nr_pages)
 	remove_pagetable(start, end, false);
 }
 
+#ifdef CONFIG_MEMORY_HOTREMOVE
 static void __meminit
 kernel_physical_mapping_remove(unsigned long start, unsigned long end)
 {
@@ -1028,7 +1029,6 @@ kernel_physical_mapping_remove(unsigned long start, unsigned long end)
 	remove_pagetable(start, end, true);
 }
 
-#ifdef CONFIG_MEMORY_HOTREMOVE
 int __ref arch_remove_memory(u64 start, u64 size)
 {
 	unsigned long start_pfn = start >> PAGE_SHIFT;