POWER9 + ARM64 Performance For Dav1d 0.8 AV1 Decoding

With last week's release of dav1d 0.8 for CPU-based AV1 video decoding we provided a number of x86_64 benchmarks while questions were raised around the ARM64 and POWER9 performance. Here are such benchmarks for those wondering about the AV1 video decoding speed on those architectures...