[RISCV] Split code that tablegen needs out of RISCVISAInfo. (#89684)

This introduces a new file, RISCVISAUtils.cpp and moves the rest of
RISCVISAInfo to the TargetParser library.

This will allow us to generate part of RISCVISAInfo.cpp using tablegen.

GitOrigin-RevId: 733a87783cfac7e6bac2c14bc3749ddca879e2be
8 files changed