[PowerPC] LSR tunings for PowerPC

The purpose of this patch is to have LSR generate better code on Power.
This is done by overriding isLSRCostLess.

Differential Revision: https://reviews.llvm.org/D40855

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326906 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed