When perfetto is enabled, u_trace_context calls driver-defined callbacks when processing trace events. Those callbacks are expected to emit perfetto trace packets. Signed-off-by: Chia-I Wu <olvaffe@gmail.com> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32360>