mn10300: make dma_cache_sync a no-op

mn10300 does not implement DMA_ATTR_NON_CONSISTENT allocations, so it
doesn't make any sense to do any work in dma_cache_sync given that it must
be a no-op when dma_alloc_attrs returns coherent memory.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>

arch/mn10300/include/asm/dma-mapping.h

@@ -11,9 +11,6 @@
 #ifndef _ASM_DMA_MAPPING_H
 #define _ASM_DMA_MAPPING_H
 
-#include <asm/cache.h>
-#include <asm/io.h>
-
 extern const struct dma_map_ops mn10300_dma_ops;
 
 static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
@@ -25,7 +22,6 @@ static inline
 void dma_cache_sync(void *vaddr, size_t size,
 		    enum dma_data_direction direction)
 {
-	mn10300_dcache_flush_inv();
 }
 
 #endif