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>

arch/arm/vfp/entry.S

@@ -17,7 +17,7 @@
  */
 #include <linux/linkage.h>
 #include <linux/init.h>
-#include <asm/constants.h>
+#include <asm/asm-offsets.h>
 #include <asm/vfpmacros.h>
 
 	.globl	do_vfp