[llvm] [TableGen][RISCV] Support sub-operands in CompressInstEmitter.cpp. (PR #133039)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp approved this pull request.

LGTM. I understand what the patch is doing now and I don't see any obvious problem, but I need more eyes.

https://github.com/llvm/llvm-project/pull/133039