PCI: Add empty stub for pci_register_io_range()

Add an empty stub for pci_register_io_range() when !CONFIG_PCI. It's needed
to convert of_pci_range_to_resource() to use IS_ENABLED(CONFIG_PCI).

Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20210527194547.1287934-2-robh@kernel.org