drm/imx: Add drm_panic support

Add support for the drm_panic module, which displays a user-friendly
message to the screen when a kernel panic occurs.

v7:
* use drm_panic_gem_get_scanout_buffer() helper

v8:
* Replace get_scanout_buffer() logic with drm_panic_set_buffer()

v9:
* Revert to using get_scanout_buffer() (Sima)
* move get_scanout_buffer() to plane helper functions

v12:
* Rename drm_panic_gem_get_scanout_buffer to drm_fb_dma_get_scanout_buffer
(Thomas Zimmermann)

Signed-off-by: Jocelyn Falempe <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Acked-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/imx/ipuv3/ipuv3-plane.c

···
 	.atomic_update = ipu_plane_atomic_update,
 };
 
+static const struct drm_plane_helper_funcs ipu_primary_plane_helper_funcs = {
+	.atomic_check = ipu_plane_atomic_check,
+	.atomic_disable = ipu_plane_atomic_disable,
+	.atomic_update = ipu_plane_atomic_update,
+	.get_scanout_buffer = drm_fb_dma_get_scanout_buffer,
+};
+
 bool ipu_plane_atomic_update_pending(struct drm_plane *plane)
 {
 	struct ipu_plane *ipu_plane = to_ipu_plane(plane);
···
 	ipu_plane->dma = dma;
 	ipu_plane->dp_flow = dp;
 
-	drm_plane_helper_add(&ipu_plane->base, &ipu_plane_helper_funcs);
+	if (type == DRM_PLANE_TYPE_PRIMARY)
+		drm_plane_helper_add(&ipu_plane->base, &ipu_primary_plane_helper_funcs);
+	else
+		drm_plane_helper_add(&ipu_plane->base, &ipu_plane_helper_funcs);
 
 	if (dp == IPU_DP_FLOW_SYNC_BG || dp == IPU_DP_FLOW_SYNC_FG)
 		ret = drm_plane_create_zpos_property(&ipu_plane->base, zpos, 0,