[llvm] [Xtensa] Implement base CallConvention. (PR #83280)

[Matt Arsenault via llvm-commits]

================
@@ -148,7 +161,13 @@ struct XtensaOperand : public MCParsedAsmOperand {
 
   bool isImm12() const { return isImm(-2048, 2047); }
 
-  bool isImm12m() const { return isImm(-2048, 2047); }
+  // Convert MOVI to literal load, when immediate is not in range (-2048, 2047)
+  bool isImm12m() const {
+    if (Kind == Immediate)
+      return true;
+
+    return false;
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arsenm wrote:

```suggestion
    return Kind == Immediate;
```

https://github.com/llvm/llvm-project/pull/83280