PCI: dwc: Move io_cfg_atu_shared to struct pcie_port

The io_cfg_atu_shared flag is set if there is an outbound iATU window used
for both config space accesses and IO port transfers.

Since the flag semantic is purely Root Port specific, it's not used in
either the DW PCIe common code or in the DW PCIe Endpoint driver. Move it
to the struct pcie_port and rename to cfg0_io_shared.

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20220624143428.8334-15-Sergey.Semin@baikalelectronics.ru


Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>