PCI: Add arch_can_pci_mmap_io() on architectures which can mmap() I/O space

This is relatively esoteric, and knowing that we don't have it makes life
easier in some cases rather than just an eventual -EINVAL from
pci_mmap_page_range().

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/include/linux/pci.h b/include/linux/pci.h
index e7bb4b62..590cfcf 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1636,6 +1636,9 @@ int pci_mmap_page_range(struct pci_dev *pdev, struct vm_area_struct *vma,
 #ifndef arch_can_pci_mmap_wc
 #define arch_can_pci_mmap_wc()		0
 #endif
+#ifndef arch_can_pci_mmap_io
+#define arch_can_pci_mmap_io()		0
+#endif
 
 #ifndef pci_root_bus_fwnode
 #define pci_root_bus_fwnode(bus)	NULL