x86/PCI: Add x86_pci_root_bus_node() to look up NUMA node from PCI bus

x86/PCI: Add x86_pci_root_bus_node() to look up NUMA node from PCI bus

The AMD early_fill_mp_bus_info() already allocates a struct pci_root_info
for each PCI host bridge it finds, and that structure contains the NUMA
node number.  We don't need to keep the same information in the
mp_bus_to_node[] table.

This adds x86_pci_root_bus_node(), which returns the NUMA node number, or
NUMA_NO_NODE if the node is unknown.

Note that unlike get_mp_bus_to_node(), x86_pci_root_bus_node() only works
for root buses.  For example, if amd_bus.c finds a host bridge on node 1 to
[bus 00-0f], get_mp_bus_to_node() returns 1 for any bus between 00 and 0f,
but x86_pci_root_bus_node() returns 1 for bus 00 and NUMA_NO_NODE for buses
01-0f.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>