presentation-time: add separate helper for zero-copy

Merged Simon Ser requested to merge emersion/wlroots:drm-drop-client-buffer-check into master

The backend is not able to tell whether a surface is being presented via direct scan-out or not. The backend will set ZERO_COPY if the buffer submitted via the output commit was presented in a zero-copy fashion, but will no know whether the buffer comes from the compositor or the client.

Merge request reports