[mlir] Fix getVectorReductionOp

1.Combining kind min/max of Vector reduction op has been changed to
  minf/maxf, minsi/maxsi, and minui/maxui. Modify getVectorReductionOp
  accordingly.
2.Add min/max to supported reductions.

Reviewed By: dcaballe, nicolasvasilache

Differential Revision: https://reviews.llvm.org/D112246