ppc/svp64: support LibreSOC architecture

ppc/svp64: support LibreSOC architecture

This patch adds support for LibreSOC machine and SVP64 extension flag
for PowerPC architecture. SV (Simple-V) is a strict RISC-paradigm
Scalable Vector Extension for the Power ISA. SVP64 is the 64-bit
Prefixed instruction format implementing SV. Funded by NLnet through EU
Grants No: 825310 and 825322, SV is in DRAFT form and is to be publicly
submitted via the OpenPOWER Foundation ISA Working Group via the
newly-created External RFC Process.

For more details, visit https://libre-soc.org.