Add xxh3 RISCV-V implementation from xxhash repo.

[BoBoDai]

This pr resolved #4471 .

Add RISCV-V implementation from xxhash repo.

Relevant performance tests are reflected in xxHash pr #1070 and #1066

I conducted testing by replacing the hash function in the fuzzer and conduct testing through qemu.

thread pool tests OK
1085 fuzzer tests completed

Although zstd does not currently use xxh3, this will better support teams who wish to use zstd and xxh3 on RISCV devices.