[AVX] Fix vpcmpeqq predicate.

Summary:
Fix vpcmpeqq predicate. AVX512 version of vpcmpeqq is not equivalent to AVX one.
Split from https://reviews.llvm.org/D32679

Reviewers: craig.topper, zvi, aymanmus

Reviewed By: craig.topper

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32786

llvm-svn: 302119