This will make PCI bridge to return zeros when accessing IO base and limit
registers, as required by PCIe base specification.

This allows to remove adhoc checks around mvebu_pcie_handle_iobase_change()
function for unsupported IO ranges. PCI_BRIDGE_EMUL_NO_IO_FORWARD ensures
that there will be no non-zeros write to IO registers when IO is not
supported.

Link: https://lore.kernel.org/r/20220104153529.31647-8-pali@kernel.orgSigned-off-by: NPali Rohár <pali@kernel.org>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NRob Herring <robh@kernel.org>