ecore_drm2: Store output in plane structure

This will simplify a bunch of API that would otherwise have to pass in
both output and plane - and in some cases we might not have the output
handy anyway.

src/lib/ecore_drm2/ecore_drm2_plane.c

@@ -104,6 +104,7 @@ out:
 
    plane->state = pstate;
    plane->type = pstate->type.value;
+   plane->output = output;
 
    DBG("FB %d assigned to Plane %d", fb->id, pstate->obj_id);
    output->planes = eina_list_append(output->planes, plane);

src/lib/ecore_drm2/ecore_drm2_private.h

@@ -711,6 +711,7 @@ struct _Ecore_Drm2_Plane
 {
    int type;
    Ecore_Drm2_Plane_State *state;
+   Ecore_Drm2_Output *output;
 };
 
 struct _Ecore_Drm2_Output_Mode