powerpc/dma: remove the unused ARCH_HAS_DMA_MMAP_COHERENT define

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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

@@ -112,7 +112,5 @@ extern int dma_set_mask(struct device *dev, u64 dma_mask);
 
 extern u64 __dma_get_required_mask(struct device *dev);
 
-#define ARCH_HAS_DMA_MMAP_COHERENT
-
 #endif /* __KERNEL__ */
 #endif	/* _ASM_DMA_MAPPING_H */