dma-mapping: bypass indirect calls for dma-direct

Avoid expensive indirect calls in the fast path DMA mapping
operations by directly calling the dma_direct_* ops if we are using
the directly mapped DMA operations.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Jesper Dangaard Brouer <brouer@redhat.com>
Tested-by: Tony Luck <tony.luck@intel.com>

arch/arc/mm/cache.c

@@ -1280,7 +1280,7 @@ void __init arc_cache_init_master(void)
 	/*
 	 * In case of IOC (say IOC+SLC case), pointers above could still be set
 	 * but end up not being relevant as the first function in chain is not
-	 * called at all for @dma_direct_ops
+	 * called at all for devices using coherent DMA.
 	 *     arch_sync_dma_for_cpu() -> dma_cache_*() -> __dma_cache_*()
 	 */
 }