openrisc: use kbuild.h instead of defining macros in asm-offset.c

This is modelled on commits such as the one below:

Commit fc1c3a003edb8a6778e64e10ef671a38c76c969e ("sh: use kbuild.h
instead of defining macros in asm-offsets.c") introduced in v2.6.26.

Signed-off-by: James Hogan <[e-mail]>
Signed-off-by: Jonas Bonn <[e-mail]>

arch/openrisc/kernel/asm-offsets.c

···
 #include <linux/mm.h>
 #include <linux/io.h>
 #include <linux/thread_info.h>
+#include <linux/kbuild.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>
-
-#define DEFINE(sym, val) \
-		asm volatile("\n->" #sym " %0 " #val : : "i" (val))
-
-#define BLANK() asm volatile("\n->" : : )
 
 int main(void)
 {