kbuild: alpha,x86_64 use generic asm-offsets.h support

Delete obsolete stuff from arch makefiles
Rename .h file to asm-offsets.h

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/alpha/lib/dbg_stackcheck.S b/arch/alpha/lib/dbg_stackcheck.S
index cc5ce3a..3c1f3e6 100644
--- a/arch/alpha/lib/dbg_stackcheck.S
+++ b/arch/alpha/lib/dbg_stackcheck.S
@@ -5,7 +5,7 @@
  * Verify that we have not overflowed the stack.  Oops if we have.
  */
 
-#include <asm/asm_offsets.h>
+#include <asm/asm-offsets.h>
 
 	.text
 	.set noat