@Kai-Heng: the problem is fixed here using your 4.4.0-99 version on my Dell Latitude E7470 with Skylake.
Well it's buggy like on 4.4.0-72, after loggin both screens go black, but I have my workaround works again. If I switch to text mode (Ctrl+Alt+F1) and back (Alt+F7) both screens work
@Kai-Heng: the problem is fixed here using your 4.4.0-99 version on my Dell Latitude E7470 with Skylake.
Well it's buggy like on 4.4.0-72, after loggin both screens go black, but I have my workaround works again. If I switch to text mode (Ctrl+Alt+F1) and back (Alt+F7) both screens work