[POWERPC] ehea: Remove dependency on MEMORY_HOTPLUG

Now that walk_memory_resource() is available regardless of
MEMORY_HOTPLUG's setting, this dependency is not needed.

Signed-off-by: Nathan Lynch <ntl@pobox.com>
Acked-by: Jeff Garzik <jeff@garzik.org>
Acked-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>