x86: remove arch specific dma_supported implementation

And instead wire it up as method for all the dma_map_ops instances.

Note that this also means the arch specific check will be fully instead
of partially applied in the AMD iommu driver.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index fc2765c..53cc0a3 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3981,6 +3981,9 @@ struct dma_map_ops intel_dma_ops = {
 	.map_page = intel_map_page,
 	.unmap_page = intel_unmap_page,
 	.mapping_error = intel_mapping_error,
+#ifdef CONFIG_X86
+	.dma_supported = x86_dma_supported,
+#endif
 };
 
 static inline int iommu_domain_cache_init(void)