[llvm] [Target] Use TableGen named argument syntax. NFC. (PR #133418)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Convert named argument comments like `/*foo=*/99`

There are more cases that could be converted, that don't use that exact syntax for the comment, like:
```
  let Src0RC32 = getVOPSrc0ForVT<Src0VT, 1/*IsTrue16*/, 0/*IsFake16*/>.ret;
```

https://github.com/llvm/llvm-project/pull/133418