[AArch64] Use PerfectShuffle costs in AArch64TTIImpl::getShuffleCost

[AArch64] Use PerfectShuffle costs in AArch64TTIImpl::getShuffleCost

Given a shuffle with 4 elements size 16 or 32, we can use the costs
directly from the PerfectShuffle tables to get a slightly more accurate
cost for the resulting shuffle.

Differential Revision: https://reviews.llvm.org/D123409