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/kernel/iwmmxt.S b/arch/arm/kernel/iwmmxt.S
index 8f74e24..24c7b04 100644
--- a/arch/arm/kernel/iwmmxt.S
+++ b/arch/arm/kernel/iwmmxt.S
@@ -17,7 +17,7 @@
 #include <linux/linkage.h>
 #include <asm/ptrace.h>
 #include <asm/thread_info.h>
-#include <asm/constants.h>
+#include <asm/asm-offsets.h>
 
 #define MMX_WR0		 	(0x00)
 #define MMX_WR1		 	(0x08)