arm: remove arch specific dma_supported implementation

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

Note that the code seems a little fishy for dmabounce and iommu, but
for now I'd like to preserve the existing behavior 1:1.

Signed-off-by: Christoph Hellwig <hch@lst.de>

arch/arm/include/asm/dma-iommu.h

@@ -35,5 +35,7 @@ int arm_iommu_attach_device(struct device *dev,
 					struct dma_iommu_mapping *mapping);
 void arm_iommu_detach_device(struct device *dev);
 
+int arm_dma_supported(struct device *dev, u64 mask);
+
 #endif /* __KERNEL__ */
 #endif