tile: handle __ro_after_init like parisc does

The tile architecture already marks RO_DATA as read-only in
the kernel, so grouping RO_AFTER_INIT_DATA with RO_DATA, as is
done by default, means the kernel faults in init when it tries
to write to RO_AFTER_INIT_DATA.  For now, just arrange that
__ro_after_init is handled like __write_once, i.e. __read_mostly.
Reviewed-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NChris Metcalf <cmetcalf@mellanox.com>

arch/tile/include/asm/cache.h

@@ -61,4 +61,7 @@
  */
 #define __write_once __read_mostly
 
+/* __ro_after_init is the generic name for the tile arch __write_once. */
+#define __ro_after_init __read_mostly
+
 #endif /* _ASM_TILE_CACHE_H */