fourier-local: stateless control modernization + HEVC strip

Compound patch carrying the fork's pre-Step-1 substrate, originally
authored by Jernej Škrabec / fourier on top of bootlin's a3c2476:

- src/h264.c + src/picture.c: V4L2_CID_MPEG_VIDEO_H264_* renamed to
  V4L2_CID_STATELESS_H264_*, struct shapes tracked to mainline
  (V4L2_CID_STATELESS_H264_DECODE_MODE/_START_CODE added to the
  passthrough shim).
- include/hevc-ctrls.h: redirect shim to <linux/v4l2-controls.h>
  (kernel-side HEVC controls now live in the canonical UAPI header).
- src/meson.build: src/h265.c / src/h265.h commented out — HEVC
  build path is excluded from this fork (RK3568 hantro G1/G2 has
  no HEVC, and the kernel-side HEVC controls have a separate
  rework in flight upstream).
- src/tiled_yuv.S: aarch64 stub for tiled_to_planar (assembly
  source was sunxi-cedrus armv7-only; aarch64 needs a stub to keep
  the build linking).
- include/h264-ctrls.h: removed (dead post-fourier — no source
  includes it; the passthrough shim's CID aliases live in the
  kernel header now).

Functionally equivalent to the prior fork master commits:
  c1f5108 V4L2_PIX_FMT_H264_SLICE rename
  4ccbfe9 Strip HEVC build path
  da9f2a5 include/h264-ctrls.h passthrough + CID aliases
  fc4bb10 src/h264.c track upstream UAPI shape
  13e9b64 src/h264.c drop num_slices field
  4d14ffb src/tiled_yuv.S aarch64 stub
  1b02c9b src/h264.c include utils.h

Folded into one commit during 2026-05-04 Step 1 reconciliation
(see ../phase0_evidence/2026-05-04/findings.md). Per-patch history
of the early fork commits preserved on the pre-step1 branch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/surface.c

@@ -46,6 +46,8 @@
 #include "v4l2.h"
 #include "video.h"
 
+bool SET_FORMAT_OF_OUTPUT_ONCE = false;
+
 VAStatus RequestCreateSurfaces2(VADriverContextP context, unsigned int format,
 				unsigned int width, unsigned int height,
 				VASurfaceID *surfaces_ids,
@@ -68,10 +70,34 @@ VAStatus RequestCreateSurfaces2(VADriverContextP context, unsigned int format,
 	bool found;
 	int rc;
 
+	//////////// HACK: this portion of the code should get cleaned up.
+
+	// v4l2_set_format needs to be called BEFORE we create any buffers
+	//
+	// we originally did this for the output stream in context.c, but 
+	// RequestCreateSurfaces2 gets called multiple times before RequestCreateContext 
+	// to allocate & map buffers. this doesn't seem to work in recent kernel versions.
+	// 
+	// we declare SET_FORMAT_OF_OUTPUT_ONCE to ensure v4l2_set_format only gets called once
+	// (in the first RequestCreateSurfaces2 call BEFORE any buffers are created later on)
+	unsigned int pixelformat = V4L2_PIX_FMT_H264_SLICE;
+	unsigned int output_type = v4l2_type_video_output(false);
+
+	if (!SET_FORMAT_OF_OUTPUT_ONCE) {
+		rc = v4l2_set_format(driver_data->video_fd, output_type, pixelformat,
+				width, height);
+		if (rc < 0) {
+			return VA_STATUS_ERROR_OPERATION_FAILED;
+		}
+
+		SET_FORMAT_OF_OUTPUT_ONCE = true;
+	}
+
+	/////////// ENDHACK
+
 	if (format != VA_RT_FORMAT_YUV420)
 		return VA_STATUS_ERROR_UNSUPPORTED_RT_FORMAT;
 
-
         if (!driver_data->video_format) {
 		found = v4l2_find_format(driver_data->video_fd,
 					 V4L2_BUF_TYPE_VIDEO_CAPTURE,