[Scalarizer] Add scalarizer support for smul.fix.sat

[Scalarizer] Add scalarizer support for smul.fix.sat

Summary:
Handle smul.fix.sat in the scalarizer. This is done by
adding smul.fix.sat to the set of "isTriviallyVectorizable"
intrinsics.

The addition of smul.fix.sat in isTriviallyVectorizable and
hasVectorInstrinsicScalarOpd can also be seen as a preparation
to be able to use hasVectorInstrinsicScalarOpd in ConstantFolding.

Reviewers: rengolin, RKSimon, dblaikie

Reviewed By: rengolin

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63704

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364177 91177308-0d34-0410-b5e6-96231b3b80d8