ARM: dma-mapping: Add macro to_dma_iommu_mapping()

This can be built without CONFIG_ARM_DMA_USE_IOMMU.
Signed-off-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

arch/arm/include/asm/device.h

@@ -27,4 +27,10 @@ struct pdev_archdata {
 #endif
 };
 
+#ifdef CONFIG_ARM_DMA_USE_IOMMU
+#define to_dma_iommu_mapping(dev) ((dev)->archdata.mapping)
+#else
+#define to_dma_iommu_mapping(dev) NULL
+#endif
+
 #endif