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/entry.S b/arch/ia64/kernel/entry.S
index 9be53e1..6d70fec 100644
--- a/arch/ia64/kernel/entry.S
+++ b/arch/ia64/kernel/entry.S
@@ -37,7 +37,7 @@
 #include <asm/cache.h>
 #include <asm/errno.h>
 #include <asm/kregs.h>
-#include <asm/offsets.h>
+#include <asm/asm-offsets.h>
 #include <asm/pgtable.h>
 #include <asm/percpu.h>
 #include <asm/processor.h>