kbuild: arm - use generic asm-offsets.h support

Delete obsoleted stuff from arch Makefile and rename
constants.h to asm-offsets.h

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/arm/mm/copypage-v4wt.S b/arch/arm/mm/copypage-v4wt.S
index 9767939..e1f2af2 100644
--- a/arch/arm/mm/copypage-v4wt.S
+++ b/arch/arm/mm/copypage-v4wt.S
@@ -14,7 +14,7 @@
  */
 #include <linux/linkage.h>
 #include <linux/init.h>
-#include <asm/constants.h>
+#include <asm/asm-offsets.h>
 
 	.text
 	.align	5