PCI hotplug: shpchp: use generic pci_configure_slot()
Use the generic pci_configure_slot() rather than the SHPC-specific
program_fw_provided_values().
Unlike the previous SHPC-specific code, pci_configure_slot() programs PCIe
settings when an _HPX method provides them, so if it's possible to have an
SHPC-managed PCIe device, it can now be configured.