powerpc/numa: Online a node if PHB is attached.

In the current design, a numa-node is made online only if that node is
attached to cpu/memory. With this design, if any PCI/IO device is found
to be attached to a numa-node which is not online then the numa-node
id of the corresponding PCI/IO device is set to NUMA_NO_NODE(-1). This
design may negatively impact the performance of PCIe device if the
numa-node assigned to PCIe device is -1 because in such case we may not
be able to accurately calculate the distance between two nodes.

The multi-controller NVMe PCIe disk has an issue with calculating the
node distance if the PCIe NVMe controller is attached to a PCI host
bridge which has numa-node id value set to NUMA_NO_NODE. This patch
helps fix this ensuring that a cpu/memory less numa node is made online
if it's attached to PCI host bridge.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240517142531.3273464-3-nilay@linux.ibm.com