PCI: Add pci_add_dma_alias() to abstract implementation

Add a pci_add_dma_alias() interface to encapsulate the details of adding an
alias.  No functional change intended.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>

include/linux/pci.h

@@ -1988,6 +1988,7 @@ static inline struct eeh_dev *pci_dev_to_eeh_dev(struct pci_dev *pdev)
 }
 #endif
 
+void pci_add_dma_alias(struct pci_dev *dev, u8 devfn);
 int pci_for_each_dma_alias(struct pci_dev *pdev,
 			   int (*fn)(struct pci_dev *pdev,
 				     u16 alias, void *data), void *data);