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/mm/copypage-v3.S

@@ -12,7 +12,7 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 #include <asm/assembler.h>
-#include <asm/constants.h>
+#include <asm/asm-offsets.h>
 
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 		.align	5