[llvm] [LoongArch] Implement COPY instruction between CFRs (PR #69300)

[WÁNG Xuěruì via llvm-commits]

================
@@ -77,6 +77,12 @@ void LoongArchInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
         .addReg(SrcReg, getKillRegState(KillSrc));
     return;
   }
+  // CFR->CRR copy.
----------------
xen0n wrote:

```suggestion
  // CFR->CFR copy.
```

https://github.com/llvm/llvm-project/pull/69300