ehea: Add DLPAR memory remove support

The eHEA driver uses the recently modified walk_memory_resource for powerpc
functionality to detect the memory layout. It further uses the memory hotplug
notifiers to catch memory hotplug events.

Signed-off-by: Hannes Hering <hering2@de.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>