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/arch/powerpc/cpu/ppc4xx/speed.c b/arch/powerpc/cpu/ppc4xx/speed.c
index 906face..4d7eb29 100644
--- a/arch/powerpc/cpu/ppc4xx/speed.c
+++ b/arch/powerpc/cpu/ppc4xx/speed.c
@@ -23,7 +23,7 @@
 
 #include <common.h>
 #include <ppc_asm.tmpl>
-#include <ppc4xx.h>
+#include <asm/ppc4xx.h>
 #include <asm/processor.h>
 
 DECLARE_GLOBAL_DATA_PTR;