[NFC] Move useSVEForFixedLengthVectors into AArch64Subtarget.h

[david-arm]

Summary

Given how small the function is and how often it gets used it
makes more sense to live in the header file.

llvm/lib/Target/AArch64/AArch64Subtarget.h

unsigned getMaxSVEVectorSizeInBits() const {
     return MaxSVEVectorSizeInBits;
   }
 
   unsigned getMinSVEVectorSizeInBits() const {
     assert(HasSVE && "Tried to get SVE vector length without SVE support!");
     return MinSVEVectorSizeInBits;
   }
 
-  bool useSVEForFixedLengthVectors() const;
+  bool useSVEForFixedLengthVectors() const {
+    // Prefer NEON unless larger SVE registers are available.
+    return hasSVE() && getMinSVEVectorSizeInBits() >= 256;
+  }
 
   unsigned getVScaleForTuning() const { return VScaleForTuning; }
 };
 } // End llvm namespace
 
 #endif

llvm/lib/Target/AArch64/AArch64Subtarget.cpp

void AArch64Subtarget::mirFileLoaded(MachineFunction &MF) const {
   // if the .mir file didn't specify it. Note that this will probably give you
   // bogus values after PEI has eliminated the callframe setup/destroy pseudo
   // instructions, specify explicitly if you need it to be correct.
   MachineFrameInfo &MFI = MF.getFrameInfo();
   if (!MFI.isMaxCallFrameSizeComputed())
     MFI.computeMaxCallFrameSize(MF);
 }
 
-bool AArch64Subtarget::useSVEForFixedLengthVectors() const {
-  // Prefer NEON unless larger SVE registers are available.
-  return hasSVE() && getMinSVEVectorSizeInBits() >= 256;
-}
-
 bool AArch64Subtarget::useAA() const { return UseAA; }