Makefile : fix generation of cpu related asm-offsets.h

commit 0edf8b5b2fa0d210ebc4d6da0fd1aceeb7e44e47 breaks
building on a different directory with the O= parameter.
The patch wil fix this issue, generating always asm-offsets.h before
the other targets.

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Matthias Weisser <weisserm@arcor.de>
CC: Wolfgang Denk <wd@denx.de>
diff --git a/board/freescale/mx35pdk/lowlevel_init.S b/board/freescale/mx35pdk/lowlevel_init.S
index 9fd04cb..698c4cf 100644
--- a/board/freescale/mx35pdk/lowlevel_init.S
+++ b/board/freescale/mx35pdk/lowlevel_init.S
@@ -21,7 +21,7 @@
 
 #include <config.h>
 #include <asm/arch/imx-regs.h>
-#include <asm/arch/asm-offsets.h>
+#include <generated/asm-offsets.h>
 #include "mx35pdk.h"
 
 /*