[regression][bisected] Virtual Reality HMDs fail to power off when SteamVR closes

Submitted by Andres Rodriguez `@lostgoat`

Assigned to Default DRI bug account

When SteamVR is closed the attached HMD no longer powers off. This is due to the display still being driven by the GPU.

The first bad commit for this behaviour is:
"drm/amd/display: Allow commits with no planes active"
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bc92c06525e5865c94256ef0227bfe870c095823

My understanding is that the commit above does fix a bug in amdgpu/dc. However, due to current Xorg versions failing to shut down outputs after re-claiming a drm lease, this commit ends up breaking userspace.

Following is the x server patch to help illustrate what X is doing incorrectly:
xorg/xserver!279 (merged)

Additional reference:
https://github.com/ValveSoftware/SteamVR-for-Linux/issues/235