[llvm] [AArch64][SME] Use entry pstate.sm for conditional streaming-mode changes (PR #152169)

[Sander de Smalen via llvm-commits]

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@@ -274,6 +277,9 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
   Register getPStateSMReg() const { return PStateSMReg; };
   void setPStateSMReg(Register Reg) { PStateSMReg = Reg; };
 
+  unsigned IsPStateSMRegUsed() const { return PStateSMRegUsed; };
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sdesmalen-arm wrote:

nit: 
```suggestion
  unsigned isPStateSMRegUsed() const { return PStateSMRegUsed; };
```

https://github.com/llvm/llvm-project/pull/152169