Previously we checked for invalid MPS settings, i.e., a device with MPS
different than its upstream bridge, in pcie_bus_detect_mps().  We only did
this if the arch or hotplug driver called pcie_bus_configure_settings(),
and then only if PCIe bus tuning was disabled (PCIE_BUS_TUNE_OFF).

Move the MPS checking code to pci_configure_device(), so we do it in the
pci_device_add() path for every device.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>