treewide: Consolidate get_dma_ops() implementations

Introduce a new architecture-specific get_arch_dma_ops() function
that takes a struct bus_type * argument. Add get_dma_ops() in
<linux/dma-mapping.h>.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Russell King <linux@armlinux.org.uk>
Cc: x86@kernel.org
Signed-off-by: Doug Ledford <dledford@redhat.com>

arch/powerpc/include/asm/ps3.h

@@ -435,7 +435,7 @@ static inline void *ps3_system_bus_get_drvdata(
 	return dev_get_drvdata(&dev->core);
 }
 
-/* These two need global scope for get_dma_ops(). */
+/* These two need global scope for get_arch_dma_ops(). */
 
 extern struct bus_type ps3_system_bus_type;