ppc4xx: Move ppc4xx headers to powerpc include directory

This patch moves some ppc4xx related headers from the common include
directory (include/) to the powerpc specific one
(arch/powerpc/include/asm/). This way to common include directory is not
so cluttered with files.

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/board/sandburst/common/flash.c b/board/sandburst/common/flash.c
index dd712e3..c65cb96 100644
--- a/board/sandburst/common/flash.c
+++ b/board/sandburst/common/flash.c
@@ -29,7 +29,7 @@
  * Sandburst Corporation
  */
 #include <common.h>
-#include <ppc4xx.h>
+#include <asm/ppc4xx.h>
 #include <asm/processor.h>