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/proc-macros.S b/arch/arm/mm/proc-macros.S
index 9137fe5..7cfc260 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -4,7 +4,7 @@
  *  VMA_VM_FLAGS
  *  VM_EXEC
  */
-#include <asm/constants.h>
+#include <asm/asm-offsets.h>
 #include <asm/thread_info.h>
 
 /*