[POWERPC] Fix build problem in ppc4xx_sgdma.c

ppc4xx_sgdma.c is #including asm/dma-mapping.h directly, which should
only ever be included via linux/dma-mapping.h.  asm/dma-mapping.h
relies on an enum defined in linux/dma-mapping.h before its own
include.  This fixes the problem.
Signed-off-by: NDavid Gibson <dwg@au1.ibm.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/ppc/syslib/ppc4xx_sgdma.c

@@ -23,11 +23,11 @@
 #include <linux/mm.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/dma-mapping.h>
 #include <linux/pci.h>
 
 #include <asm/system.h>
 #include <asm/io.h>
-#include <asm/dma-mapping.h>
 #include <asm/ppc4xx_dma.h>
 
 void