[AArch64] Don't allow mixed partial reductions without i8mm (llvm#137602)

Partial reductions with mixed extends should only be allowed if i8mm is
present.

Author: SamTebbs33

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -5401,11 +5401,10 @@ InstructionCost AArch64TTIImpl::getPartialReductionCost(
   } else
     return Invalid;
 
-  // AArch64 supports lowering mixed extensions to a usdot but only if the
-  // i8mm or sve/streaming features are available.
+  // AArch64 supports lowering mixed fixed-width extensions to a usdot but only
+  // if the i8mm feature is available.
   if (OpAExtend == TTI::PR_None || OpBExtend == TTI::PR_None ||
-      (OpAExtend != OpBExtend && !ST->hasMatMulInt8() &&
-       !ST->isSVEorStreamingSVEAvailable()))
+      (OpAExtend != OpBExtend && !ST->hasMatMulInt8()))
     return Invalid;
 
   if (!BinOp || *BinOp != Instruction::Mul)