ampere-av1 Phase 2 step 4: AV1 dispatch scaffolding compiles and wires

surface.h: av1 substruct (picture + tile_group_entries[AV1_MAX_TILES=128]
  + num_tile_group_entries counter)
picture.c: dispatch VAPictureParameterBufferAV1 + VASliceParameterBufferAV1
  into surface->params.av1.*; call av1_set_controls in EndPicture path
av1.h: minimal interface (av1_set_controls signature)
av1.c: stub set_controls returning -1 with diagnostic; _Static_assert on
  v4l2_ctrl_av1_tile_group_entry size = 16 (Janet hygiene)
meson.build: av1.c + av1.h in source list

Verified on ampere with /tmp/test_av1.ivf via LIBVA_DRIVER_NAME=v4l2_request:

  v4l2-request: ampere-av1: vpu981 AV1 decoder at /dev/video4 + /dev/media3
  v4l2-request: ampere-av1: av1_set_controls stub — Phase 2.1 will implement ...
  [av1] Failed to end picture decode issue: 1 (operation failed).
  [av1] HW accel end frame fail.
  [dec:av1] Error submitting packet to decoder: Input/output error

Clean graceful failure — vpu981 probe works, dispatch reaches av1.c,
stub returns ERROR, ffmpeg falls back to SW. No crash, no IOMMU fault,
no kernel taint.

Next: Phase 2.1 implementation of fill_sequence + fill_frame +
fill_film_grain + fill_tile_group_entries (~700 LoC mirror of Kwiboo
v4l2_request_av1.c, applying F1/F2/F3 implementation-time corrections
from Janet review v2).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/av1.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2026 claude-noether <claude-noether@reauktion.de>
+ *
+ * ampere-av1-enablement Phase 2: AV1 codec dispatcher header for libva-
+ * v4l2-request-fourier. Mirrors vp9.h shape — single set_controls entry
+ * point that translates surface->params.av1.* VAAPI structures into a
+ * batch of V4L2_CID_STATELESS_AV1_{SEQUENCE,FRAME,TILE_GROUP_ENTRY,
+ * FILM_GRAIN} controls + the underlying request_fd / OUTPUT plane setup.
+ *
+ * V4L2 target: V4L2_PIX_FMT_AV1_FRAME on the vpu981 hantro instance
+ * (RK3588's dedicated AV1 decoder).
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sub license, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial portions
+ * of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
+ * THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef _AV1_H_
+#define _AV1_H_
+
+#include "context.h"
+#include "request.h"
+#include "surface.h"
+
+int av1_set_controls(struct request_data *driver_data,
+		     struct object_context *context,
+		     struct object_surface *surface);
+
+#endif /* _AV1_H_ */