[llvm] [TableGen][NFC] Replace hardcoded opcode numbering. (PR #81065)

[Jason Eckhardt via llvm-commits]

nvjle wrote:

Hi @wangpc-pp (or anyone else interested)-- this NFC patch just updates a couple instances of the hardcoded enum value setting with `CodeGenTarget::getInstrIntValue` (introduced in PR #80486) to eliminate duplicate code. If someone would kindly commit on my behalf, thank you.

https://github.com/llvm/llvm-project/pull/81065