powerpc: Swiotlb breaks pseries

Turning on SWIOTLB selects or enables PPC_NEED_DMA_SYNC_OPS, which means
we get the non empty versions of dma_sync_* in asm/dma-mapping.h

On my pseries machine the dma_ops have no such routines and we die with
a null pointer - this patch gets it booting, is there a more elegant way
to do it?
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/dma-mapping.h

@@ -309,6 +309,8 @@ static inline void dma_sync_single_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_single_range_for_cpu)
 		dma_ops->sync_single_range_for_cpu(dev, dma_handle, 0,
 					   size, direction);
 }
@@ -320,6 +322,8 @@ static inline void dma_sync_single_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_single_range_for_device)
 		dma_ops->sync_single_range_for_device(dev, dma_handle,
 					      0, size, direction);
 }
@@ -331,6 +335,8 @@ static inline void dma_sync_sg_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_sg_for_cpu)
 		dma_ops->sync_sg_for_cpu(dev, sgl, nents, direction);
 }
 
@@ -341,6 +347,8 @@ static inline void dma_sync_sg_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_sg_for_device)
 		dma_ops->sync_sg_for_device(dev, sgl, nents, direction);
 }
 
@@ -351,6 +359,8 @@ static inline void dma_sync_single_range_for_cpu(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_single_range_for_cpu)
 		dma_ops->sync_single_range_for_cpu(dev, dma_handle,
 					   offset, size, direction);
 }
@@ -362,6 +372,8 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
 	struct dma_mapping_ops *dma_ops = get_dma_ops(dev);
 
 	BUG_ON(!dma_ops);
+
+	if (dma_ops->sync_single_range_for_device)
 		dma_ops->sync_single_range_for_device(dev, dma_handle, offset,
 					      size, direction);
 }