src/tiled_yuv.S: stub tiled_to_planar on aarch64

The whole body of tiled_yuv.S is wrapped in #ifndef __aarch64__ — the
ARMv7 NEON Thumb code doesn't assemble on aarch64. On 64-bit ARM the
.S object is therefore empty and tiled_to_planar comes out as an
undefined symbol in the .so, which dlopen rejects at vainfo time:

  libva error: dlopen ... failed: undefined symbol: tiled_to_planar

Runtime-wise, tiled_to_planar is only called when
video_format_is_linear() returns false, which only happens for the
sunxi-cedrus DRM_FORMAT_MOD_ALLWINNER_TILED NV12 entry — never on
hantro/rkvdec. So the right fix is a no-op stub on aarch64 just to
satisfy the linker.

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

src/tiled_yuv.S

@@ -182,4 +182,19 @@ thumb_function tiled_deinterleave_to_planar
 	b	7b
 end_function tiled_deinterleave_to_planar
 
+#else /* __aarch64__ */
+
+/* Fourier-local: aarch64 stub. The body of this file is ARMv7 NEON Thumb
+ * assembly used by sunxi-cedrus (Allwinner-tiled NV12 → linear NV12) and
+ * is never reached on aarch64 hosts because video_format_is_linear()
+ * returns true for our NV12 entries. Provide a stub so the shared object
+ * still resolves the symbol; if ever actually called, return immediately. */
+.text
+.global tiled_to_planar
+.type tiled_to_planar, %function
+.hidden tiled_to_planar
+tiled_to_planar:
+	ret
+.size tiled_to_planar, .-tiled_to_planar
+
 #endif