[FFmpeg-devel] Optimize H264 decoding for loongarch.

[Hao Chen]

./ffmpeg -i 1_h264_1080p_30fps_3Mbps.mp4 -f rawvideo -y /dev/null -an
before: 170fps
after : 296fps

V2: Update loongson_intrinsics.h to 1.0.3 in patch 2/7.
V3: Resubmit these patches due to the encoding problem of the last
email.

[PATCH v3 1/7] avutil: [loongarch] Add support for loongarch SIMD.
[PATCH v3 2/7] avcodec: [loongarch] Optimize h264_chroma_mc with LASX.
[PATCH v3 3/7] avcodec: [loongarch] Optimize h264qpel with LASX.
[PATCH v3 4/7] avcodec: [loongarch] Optimize h264dsp with LASX.
[PATCH v3 5/7] avcodec: [loongarch] Optimize h264idct with LASX.
[PATCH v3 6/7] avcodec: [loongarch] Optimize h264_deblock with LASX.
[PATCH v3 7/7] avcodec: [loongarch] Optimize pred16x16_plane with LASX.