spapr: Use DT memory node rendering helper for other nodes This finishes refactoring by using the spapr_populate_memory_node helper for all nodes and removing leftovers from spapr_populate_memory(). This is not a part of the previous patch because the patches look nicer apart. Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Signed-off-by: Alexander Graf <agraf@suse.de>