powerpc/dma: Add optional platform override of dma_set_mask()

Some platforms may want to override dma_set_mask() to take into
account some specific "features" such as the availability of
a direct-map window in addition to an iommu.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/machdep.h

@@ -102,6 +102,9 @@ struct machdep_calls {
 	void		(*pci_dma_dev_setup)(struct pci_dev *dev);
 	void		(*pci_dma_bus_setup)(struct pci_bus *bus);
 
+	/* Platform set_dma_mask override */
+	int		(*dma_set_mask)(struct device *dev, u64 dma_mask);
+
 	int		(*probe)(void);
 	void		(*setup_arch)(void); /* Optional, may be NULL */
 	void		(*init_early)(void);