[TTI][X86] update costs of interleaved load\store of i64\double

This patch contains more accurate cost of interelaved load\store of stride 2 for the types int64\double on AVX2.

Reviewers: delena, RKSimon, craig.topper, dorit

Reviewed By: dorit

Differential Revision: https://reviews.llvm.org/D40008

llvm-svn: 318385