Avoid compile warnings on non-default arm64 configs

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Merge tag 'dma-mapping-4.20-2' of git://git.infradead.org/users/hch/dma-mapping

Pull dma-mapping fix from Christoph Hellwig:
 "Avoid compile warnings on non-default arm64 configs"

* tag 'dma-mapping-4.20-2' of git://git.infradead.org/users/hch/dma-mapping:
  arm64: fix warnings without CONFIG_IOMMU_DMA

arch/arm64/mm/dma-mapping.c

@@ -160,6 +160,7 @@ void arch_sync_dma_for_cpu(struct device *dev, phys_addr_t paddr,
 	__dma_unmap_area(phys_to_virt(paddr), size, dir);
 }
 
+#ifdef CONFIG_IOMMU_DMA
 static int __swiotlb_get_sgtable_page(struct sg_table *sgt,
 				      struct page *page, size_t size)
 {
@@ -188,6 +189,7 @@ static int __swiotlb_mmap_pfn(struct vm_area_struct *vma,
 
 	return ret;
 }
+#endif /* CONFIG_IOMMU_DMA */
 
 static int __init atomic_pool_init(void)
 {