[PGO][PGSO] TargetLowering/TargetTransformationInfo/SwitchLoweringUtils part.

Summary:
(Split of off D67120)

TargetLowering/TargetTransformationInfo/SwitchLoweringUtils changes for profile
guided size optimization.

Reviewers: davidxl

Subscribers: eraman, hiraditya, haicheng, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69580