compositor: do not schedule repaint when enabling output
When the compositor enables a weston output, it also damages the entire output. The damaging schedules a repaint of the entire output, which results in a modeset for the drm_output. While setting the damage region of the output is necessary to ensure that the output is redrawn, the repaint is not necessary before any client is shown on the output. However, the modeset will prevent a fullscreen client with a different pixel format (e.g. NV12) than the renderer from being put directly on a plane.
Set the damage region of the weston output, but do not schedule a repaint when enabling a weston output.