[AVX512][AVX2]Cost calculation for interleave load/store patterns {v8i8,v16i8,v32i8,v64i8}

This patch adds accurate instructions cost.
The formula presents two cases(stride 3 and stride 4) and calculates the cost according to the VF and stride.

Reviewers:
1. delena
2. Farhana
3. zvi
4. dorit
5. Ayal

Differential Revision: https://reviews.llvm.org/D38762

Change-Id: If4cfbd4ac0e63694e8144cb78c7fa34850647ff7
llvm-svn: 316072