iommu: Export and rename iommu_group_get_for_pci_dev()

Rename that function to pci_device_group() and export it, so
that IOMMU drivers can use it as their device_group
call-back.

Signed-off-by: Joerg Roedel <jroedel@suse.de>

include/linux/iommu.h

@@ -317,6 +317,9 @@ static inline size_t iommu_map_sg(struct iommu_domain *domain,
 	return domain->ops->map_sg(domain, iova, sg, nents, prot);
 }
 
+/* PCI device grouping function */
+extern struct iommu_group *pci_device_group(struct device *dev);
+
 #else /* CONFIG_IOMMU_API */
 
 struct iommu_ops {};