lavu/hwcontext_drm: preparations for RKMPP hwcontext

Signed-off-by: nyanmisaka <nst799610810@gmail.com>

libavutil/hwcontext_drm.h

@@ -50,6 +50,12 @@ typedef struct AVDRMObjectDescriptor {
      * DRM PRIME fd for the object.
      */
     int fd;
+    /**
+     * DRM PRIME mapped virtual ptr for above fd.
+     *
+     * The content of this buffer must be readonly when acting decoder's out buffer.
+     */
+    void *ptr;
     /**
      * Total size of the object.
      *
@@ -63,6 +69,10 @@ typedef struct AVDRMObjectDescriptor {
      * DRM_FORMAT_MOD_INVALID.
      */
     uint64_t format_modifier;
+    /**
+     * User opaque for the object.
+     */
+    void *opaque;
 } AVDRMObjectDescriptor;
 
 /**