[SVE] Eliminate calls to default-false VectorType::get() from AArch64

[ctetreau]

ping?

[efriedma]

LGTM

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

int AArch64TTIImpl::getInterleavedMemoryOpCost(unsigned Opcode, Type *VecTy,
                                                bool UseMaskForCond,
                                                bool UseMaskForGaps) {
   assert(Factor >= 2 && "Invalid interleave factor");
   auto *VecVTy = cast<VectorType>(VecTy);
 
   if (!UseMaskForCond && !UseMaskForGaps &&
       Factor <= TLI->getMaxSupportedInterleaveFactor()) {
     unsigned NumElts = VecVTy->getNumElements();
-    auto *SubVecTy = VectorType::get(VecTy->getScalarType(), NumElts / Factor);
+    auto *SubVecTy =
+        FixedVectorType::get(VecTy->getScalarType(), NumElts / Factor);
 
     // ldN/stN only support legal vector types of size 64 or 128 in bits.
     // Accesses having vector types that are a multiple of 128 bits can be
     // matched to more than one ldN/stN instruction.
     if (NumElts % Factor == 0 &&
         TLI->isLegalInterleavedAccessType(SubVecTy, DL))
       return Factor * TLI->getNumInterleavedAccesses(SubVecTy, DL);
   }