[RISCV][NFC] Move compressInst/uncompressInst to RISCVBaseInfo

We have several usages of compressInst/uncompressInst in different
files, which results in duplicated code. We move their implementations
to RISCVBaseInfo under namespace RISCVRVC to remove these duplications.

Reviewed By: craig.topper, asb

Differential Revision: https://reviews.llvm.org/D141897