PCI: designware: Keep viewport fixed for IO transaction if num_viewport > 2

Most of the platforms have 3 or more viewports.  For such platforms, We do
not need to share viewports between IO and CFG.  Assign viewport 2 to IO
transactions in such cases.

Tested-by: Dong Bo <dongbo4@huawei.com>
Signed-off-by: Pratyush Anand <pratyush.anand@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rob Herring <robh@kernel.org>

drivers/pci/host/pcie-designware.h

@@ -44,6 +44,7 @@ struct pcie_port {
 	struct resource		*busn;
 	int			irq;
 	u32			lanes;
+	u32			num_viewport;
 	struct pcie_host_ops	*ops;
 	int			msi_irq;
 	struct irq_domain	*irq_domain;