[llvm] [Mips] Allow expressions in some immediate operands (PR #127581)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> LGTM for the code. But there is some code format warning.

Thanks. I prefer to ignore the formatting warning. I do not touch these lines and do not want to format them (unneeded diff).

```
unsigned MipsMCCodeEmitter::
getExprOpValue(const MCExpr *Expr, SmallVectorImpl<MCFixup> &Fixups,
               const MCSubtargetInfo &STI) const {
```

https://github.com/llvm/llvm-project/pull/127581