dma-mapping: turn dma_cache_sync into a dma_map_ops method

After we removed all the dead wood it turns out only two architectures
actually implement dma_cache_sync as a real op: mips and parisc.  Add
a cache_sync method to struct dma_map_ops and implement it for the
mips defualt DMA ops, and the parisc pa11 ops.

Note that arm, arc and openrisc support DMA_ATTR_NON_CONSISTENT, but
never provided a functional dma_cache_sync implementations, which
seems somewhat odd.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

arch/m68k/include/asm/dma-mapping.h

@@ -8,10 +8,4 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
         return &m68k_dma_ops;
 }
 
-static inline void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
-				  enum dma_data_direction dir)
-{
-	/* we use coherent allocation, so not much to do here. */
-}
-
 #endif  /* _M68K_DMA_MAPPING_H */