PCI: Add pci_set_acpi_fwnode() to set ACPI_COMPANION

Move the existing logic from acpi_pci_bridge_d3() to a separate function
pci_set_acpi_fwnode() to set the ACPI fwnode.  No functional change
intended.

Link: https://lore.kernel.org/r/20210817180500.1253-7-ameynarkhede03@gmail.com


Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>