Funnel the actual TargetTransformInfo pass from the SelectionDAGISel
pass into the SelectionDAG itself rather than snooping on the
implementation of that pass as exposed by the TargetMachine. This
removes the last direct client of the ScalarTargetTransformInfo class
outside of the TTI pass implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171625 91177308-0d34-0410-b5e6-96231b3b80d8