Hardcode "non-desktop" RandR property name

It's a bit silly to require current randrproto just for this definition,
which can't really change anyway.

Suggested-by: Qiang Yu <qiang.yu@amd.com>
(Ported from amdgpu commit ae8e02c6fc4ef5d5340b8cd4739e66b19b9e3386)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>