[Intel-gfx] USB-C to HDMI adapters unusable on Linux, fine on Win10

[Daniel J Blueman]

With KBL/SKL and USB-C (DP) to HDMI adapters, we still see
rainbow-like colours on external devices [1] under Linux, though the
issue doesn't reproduce on Windows.

Let me know of any suggestions/patches/changes I can try to aid in
debugging this.

Thanks!
  Daniel

[1] https://bugs.freedesktop.org/show_bug.cgi?id=99137
-- 
Daniel J Blueman