drm/vboxvideo: Implement struct drm_mode_config_funcs.mode_valid

The implementation of struct drm_mode_config_funcs.mode_valid verifies
that enough video memory is available for a given display mode.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200203155258.9346-5-tzimmermann@suse.de

drivers/gpu/drm/vboxvideo/vbox_mode.c

@@ -826,6 +826,7 @@ static int vbox_connector_init(struct drm_device *dev,
 
 static const struct drm_mode_config_funcs vbox_mode_funcs = {
 	.fb_create = drm_gem_fb_create_with_dirty,
+	.mode_valid = drm_vram_helper_mode_valid,
 	.atomic_check = drm_atomic_helper_check,
 	.atomic_commit = drm_atomic_helper_commit,
 };