Patch to cherry-pick from master into 1.19 branch

[Ilia Mirkin]

On Tue, Apr 3, 2018 at 11:17 AM, Mario Kleiner
<mario.kleiner.de at gmail.com> wrote:
> Hi Adam,
>
> b5f9fcd50a999a00128c0cc3f6e7d1f66182c9d5 ("xfree86/modes: Adapt
> xf86Randr12CrtcComputeGamma() for depth 30. (v2)")
>
> would be really good to have in server 1.19.7, so xf86-video-intel/nouveau
> can operate at screen depth 30 and keep gamma table updates via
> xf86vidmode and randr functional, instead of the server switching to
> identity gamma ramps for the whole depth 30 session and other weirdness.

FWIW it works fine with the identity ramps, so it is not such a huge
problem. I did run into issues when I applied Mario's patch to
xf86-video-nouveau and xorg 1.19.x:
https://lists.freedesktop.org/archives/nouveau/2018-March/030013.html

Perhaps the nouveau patch should just be predicated on xorg 1.20? We
still want to support older X servers, so we'll need some kind of
version check anyways.

  -ilia