dma-mapping: merge direct and noncoherent ops

All the cache maintainance is already stubbed out when not enabled,
but merging the two allows us to nicely handle the case where
cache maintainance is required for some devices, but not others.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Paul Burton <paul.burton@mips.com> # MIPS parts

include/asm-generic/dma-mapping.h

@@ -4,16 +4,7 @@
 
 static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 {
-	/*
-	 * Use the non-coherent ops if available.  If an architecture wants a
-	 * more fine-grained selection of operations it will have to implement
-	 * get_arch_dma_ops itself or use the per-device dma_ops.
-	 */
-#ifdef CONFIG_DMA_NONCOHERENT_OPS
-	return &dma_noncoherent_ops;
-#else
 	return &dma_direct_ops;
-#endif
 }
 
 #endif /* _ASM_GENERIC_DMA_MAPPING_H */