[Hexagon] Generate TargetConstant in SelectAnyInt

At some point in instruction selection, A2_tfrsi Constant:i32<...> was
created, where the "Constant" came from SelectAnyInt. Since it wasn't
a TargetConstant, it was selected again, leading to
  %vreg = A2_tfrsi ...
  ...   = A2_tfrsi %vreg
which is not a valid code.