memory-hotplug: export the function try_offline_node() fix

memory-hotplug: export the function try_offline_node() fix

"memory-hotplug: export the function try_offline_node()" declares
try_offline_node() for CONFIG_MEMORY_HOTPLUG, but this function is only
defined for CONFIG_MEMORY_HOTREMOVE:

ERROR: "try_offline_node" [drivers/acpi/processor.ko] undefined!

Fix the build by definining it appropriately.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>