Backport to 9.0.0 of: backend-drm: schedule connector disable for detached head

[Martin Petzold]

Has anyone backported this [1] patch to Weston 9.0.0?
[1] 
https://gitlab.freedesktop.org/wayland/weston/-/commit/bcacd9ec5a924317416eabb65a6cd6767d5bfb94

Thanks,

Martin