Arc A380: HEVC Main (8-bit) hardware decoding not working via VAAPI

[Ale-1970]

Hardware:

• GPU: Intel Arc A380
• Driver: intel-media-va-driver 25.2.3+dfsg1-1 (iHD_drv_video.so)
• Kernel: [aggiungi output di uname -r]
• OS: Debian 13 (Trixie) / LXC container

Issue:
HEVC Main profile (8-bit) hardware decoding is not working via VAAPI.
ffmpeg falls back to software decoder even with -hwaccel vaapi flag.

HEVC Main 10 profile (10-bit) works correctly with hardware acceleration.

vainfo output:

VAProfileHEVCMain      : VAEntrypointVLD
VAProfileHEVCMain10    : VAEntrypointVLD

Test:

# Generate 8-bit HEVC test file
ffmpeg -f lavfi -i testsrc=duration=10:size=1920x800:rate=24 \
       -c:v libx265 -preset fast -pix_fmt yuv420p test_8bit.mp4

# Try hardware decode
ffmpeg -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 \
       -i test_8bit.mp4 -f null -

Expected: Hardware decoder usage (vaapi surface)
Actual: Software fallback hevc (native) -> wrapped_avframe

Note: HEVC Main 10 (10-bit) works fine:

ffmpeg -hwaccel vaapi -hwaccel_device /dev/dri/renderD128 \
       -hwaccel_output_format vaapi \
       -i test_10bit.mkv -c:v av1_vaapi output.mkv
# This works perfectly with full hardware pipeline

**Request**: Please investigate HEVC Main (8-bit) decoder support for Arc A380.