Optimize the put and avg filtering for 8x8 chroma blocks

Signed-off-by: Arnie Chang <arnie.chang@sifive.com>
---
 libavcodec/h264chroma.c                   |   2 +
 libavcodec/h264chroma.h                   |   1 +
 libavcodec/riscv/Makefile                 |   3 +
 libavcodec/riscv/h264_chroma_init_riscv.c |  39 ++
 libavcodec/riscv/h264_mc_chroma.S         | 492 ++++++++++++++++++++++
 libavcodec/riscv/h264_mc_chroma.h         |  34 ++
 6 files changed, 571 insertions(+)
 create mode 100644 libavcodec/riscv/h264_chroma_init_riscv.c
 create mode 100644 libavcodec/riscv/h264_mc_chroma.S
 create mode 100644 libavcodec/riscv/h264_mc_chroma.h