drm/imx: switch to universal planes

Use drm_universal_plane_init to create the planes, create the primary
plane first and use drm_crtc_init_with_planes to associate it with
the crtc.
This gets rid of the unused fallback primary plane previously created
by drm_crtc_init and fixes a NULL pointer dereference issue that can
be triggered by a modeset from userspace when fbdev helpers are
enabled [1].

[1] https://lkml.org/lkml/2015/11/4/107

Reported-by: Liu Ying <Ying.Liu@freescale.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Liu Ying <Ying.Liu@freescale.com>
diff --git a/drivers/gpu/drm/imx/imx-drm.h b/drivers/gpu/drm/imx/imx-drm.h
index 28e776d..83284b4 100644
--- a/drivers/gpu/drm/imx/imx-drm.h
+++ b/drivers/gpu/drm/imx/imx-drm.h
@@ -9,6 +9,7 @@
 struct drm_encoder;
 struct drm_fbdev_cma;
 struct drm_framebuffer;
+struct drm_plane;
 struct imx_drm_crtc;
 struct platform_device;
 
@@ -24,7 +25,7 @@
 };
 
 int imx_drm_add_crtc(struct drm_device *drm, struct drm_crtc *crtc,
-		struct imx_drm_crtc **new_crtc,
+		struct imx_drm_crtc **new_crtc, struct drm_plane *primary_plane,
 		const struct imx_drm_crtc_helper_funcs *imx_helper_funcs,
 		struct device_node *port);
 int imx_drm_remove_crtc(struct imx_drm_crtc *);