[LoopVectorizer] Use TTI.getOperandInfo()

Call getOperandInfo() instead of using (near) duplicated code in
LoopVectorizationCostModel::getInstructionCost().

This gets the OperandValueKind and OperandValueProperties values for a Value
passed as operand to an arithmetic instruction.

getOperandInfo() used to be a static method in TargetTransformInfo.cpp, but
is now instead a public member.

Review: Florian Hahn
https://reviews.llvm.org/D52883

llvm-svn: 343852