[llvm] [RISCV] Reorder RISCVInstrInfoXCV.td to separate Operands, SDNodeXForms, formats, and instructions into separate sections. NFC (PR #131411)

[Alex Bradbury via llvm-commits]

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

I'm assuming/hoping we have enough test coverage that any obvious copy and paste errors will be picked up (though I have of course scanned through and saw nothing that stood out).

This LGTM, and is indeed much more consistent with how we structure other similar files.

https://github.com/llvm/llvm-project/pull/131411