IBM Linux on z SIMD optimization

**Is your feature request related to a problem? Please describe.**
IBM z architecture provides SIMD capabilities that can be utilized for zstd optimization similar to SSE and Neon SIMD optimizations that have been contributrd to zstd.

**Describe the solution you'd like**
Optimize zstd to utilize IBMz VX SIMD intrinsics in zstd_lazy.c and ztsd_compress.c equivalent to optimization for SSE and Neon.

**Describe alternatives you've considered**
Because zstd has implemented architecture-specific optimizations for other architectures, a hand-coded implementation has been shown to provide unique benefits above auto-vectorization.

**Additional context**
Financial bounty from IBM available for negotiation. Inquiries from interested developers welcome.