kbuild: ia64 use generic asm-offsets.h support

Delete obsolete stuff from arch Makefile
Rename file to asm-offsets.h
The trick used in the arch Makefile to circumvent the circular
dependency is kept.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/arch/ia64/kernel/head.S b/arch/ia64/kernel/head.S
index 8d3a929..bfe65b2 100644
--- a/arch/ia64/kernel/head.S
+++ b/arch/ia64/kernel/head.S
@@ -25,7 +25,7 @@
 #include <asm/fpu.h>
 #include <asm/kregs.h>
 #include <asm/mmu_context.h>
-#include <asm/offsets.h>
+#include <asm/asm-offsets.h>
 #include <asm/pal.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>