X86 Tests: Update more isel tests with FastVariableShuffle feature

Summary:
Added the FastVariableShuffle feature to cases that resembled processors
for which this fearure is on.
For AVX2 there are processors with and w/o this fearue enable.
For AVX512 only KNL does enable this feature so cases which only have
+avx512f were left without the FastVariableShuffle enabled.

Reviewers: RKSimon, craig.topper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41851

llvm-svn: 322090