[NFC][SCEV] Piping to pass TTI into SCEVExpander::isHighCostExpansionHelper()

Summary:
Future patches will make use of TTI to perform cost-model-driven `SCEVExpander::isHighCostExpansionHelper()`
This is a fully NFC patch to make things reviewable.

Reviewers: reames, mkazantsev, wmi, sanjoy

Reviewed By: mkazantsev

Subscribers: hiraditya, zzheng, javed.absar, dmgreen, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73704