[llvm] [LoongArch] Add support for the ud macro instruction (PR #171583)

[Lu Weining via llvm-commits]

================
@@ -157,6 +157,29 @@ static DecodeStatus decodeSImmOperand(MCInst &Inst, uint64_t Imm,
   return MCDisassembler::Success;
 }
 
+// Decode AMOSWAP.W and UD, which share the same base encoding.
----------------
SixWeining wrote:

```suggestion
// Decode AMSWAP.W and UD, which share the same base encoding.
```

https://github.com/llvm/llvm-project/pull/171583