drm/panic: Add a private field to struct drm_scanout_buffer

This allows driver to set some private data in get_scanout_buffer(),
and re-use them in set_pixel() callback.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20250624091501.257661-2-jfalempe@redhat.com
Signed-off-by: Maarten Lankhorst <dev@lankhorst.se>

include/drm/drm_panic.h

@@ -72,6 +72,12 @@ struct drm_scanout_buffer {
 	void (*set_pixel)(struct drm_scanout_buffer *sb, unsigned int x,
 			  unsigned int y, u32 color);
 
+	/**
+	 * @private: private pointer that you can use in the callbacks
+	 * set_pixel()
+	 */
+	void *private;
+
 };
 
 #ifdef CONFIG_DRM_PANIC