nios2: Add types.h header required for __u32 type

Reported by the header checker (CONFIG_HEADERS_CHECK=y):

  CHECK   usr/include/asm/ (31 files)
./usr/include/asm/ptrace.h:77: found __[us]{8,16,32,64} type without #include <linux/types.h>

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Ley Foon Tan <lftan@altera.com>