PCI: Export pci_pio_to_address() for module use

This interface will be used by PCI host drivers for PIO translation,
export it to support compiling those drivers as kernel modules.

Link: https://lore.kernel.org/r/20210420061723.989-3-jianjun.wang@mediatek.com


Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>