Add support for linux-drm-syncobj-v1

[emersion]

Depends on https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4715

[SMFloris]

Going to test it out fully later today, but I do get a compiler error currently on the condition: server->features.timeline.

I know this is a draft - so is this just a placeholder to have a check on the timeline feature?

Thanks for your contribution!

[SMFloris]

Made the condition server->features.timeline true; I think it sort of improved the flickering, but certainly not made it go away. Tested it with the latest 560 driver. Meanwhile, had to switch to KDE + Egl where the flickering is completely gone.

[c2h5oh]

We might still be missing some implementation bits https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4715

[SMFloris]

@c2h5oh , ah indeed completely missed that.

Oh well, I'll wait for more progress on that merge request and test more as things are moving forward. I don't know about you guys, but I'm feeling pretty optimistic!