spapr: Clean up device node name generation for PCI devices

spapr: Clean up device node name generation for PCI devices

spapr_populate_pci_child_dt() adds a 'name' property to the device tree
node for PCI devices.  This is never necessary for a flattened device tree,
it is implicit in the name added when the node is constructed.  In fact
anything we do add to a 'name' property will be overwritten with something
derived from the structural name in the guest firmware (but in fact it is
exactly the same bytes).

So, remove that.  In addition, pci_get_node_name() is very simple, so fold
it into its (also simple) sole caller spapr_create_pci_child_dt().

While we're there rename pci_find_device_name() to the shorter and more
accurate dt_name_from_class().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>