drm: sti: fix module compilation issue

When compiling in module some symbol aren't missing,
export them correctly.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/sti/sti_drm_plane.c

@@ -194,3 +194,4 @@ struct drm_plane *sti_drm_plane_init(struct drm_device *dev,
 
 	return &layer->plane;
 }
+EXPORT_SYMBOL(sti_drm_plane_init);

drivers/gpu/drm/sti/sti_hqvdp.c

@@ -816,6 +816,7 @@ struct sti_layer *sti_hqvdp_create(struct device *dev)
 
 	return &hqvdp->layer;
 }
+EXPORT_SYMBOL(sti_hqvdp_create);
 
 static void sti_hqvdp_init_plugs(struct sti_hqvdp *hqvdp)
 {

drivers/gpu/drm/sti/sti_layer.c

@@ -40,6 +40,7 @@ const char *sti_layer_to_str(struct sti_layer *layer)
 		return "<UNKNOWN LAYER>";
 	}
 }
+EXPORT_SYMBOL(sti_layer_to_str);
 
 struct sti_layer *sti_layer_create(struct device *dev, int desc,
 				   void __iomem *baseaddr)
@@ -77,6 +78,7 @@ struct sti_layer *sti_layer_create(struct device *dev, int desc,
 
 	return layer;
 }
+EXPORT_SYMBOL(sti_layer_create);
 
 int sti_layer_prepare(struct sti_layer *layer,
 		      struct drm_crtc *crtc,