Add Mediatek nor flash node

Signed-off-by: Bayi Cheng <bayi.cheng@mediatek.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium. org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>