[AArch64][GlobalISel] Add legalization for vecreduce.fmul (#73309)

There are no native operations that we can use for floating point mul,
so lower by splitting the vector into chunks multiple times. There is
still a missing fold for fmul_indexed, that could help the gisel test
cases a bit.
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 37e7153..f2eb32e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -2831,6 +2831,7 @@
     return Legalized;
   }
   case TargetOpcode::G_VECREDUCE_FADD:
+  case TargetOpcode::G_VECREDUCE_FMUL:
   case TargetOpcode::G_VECREDUCE_FMIN:
   case TargetOpcode::G_VECREDUCE_FMAX:
   case TargetOpcode::G_VECREDUCE_FMINIMUM: