[llvm] [RISCV][Disassembler] Use a table to store all the decoder tables and their associated features. NFC (PR #130883)

[Sam Elliott via llvm-commits]

https://github.com/lenary approved this pull request.

LGTM. Thanks for the name update.

Agreed that it's simplest to just always invoke addSPOperands.

https://github.com/llvm/llvm-project/pull/130883