[X86][AVX512] Fix build fail after D81548

Test function mask_cmp_128 failed during ISEL
LLVM ERROR: Cannot select: t37: v8i1 = X86ISD::KSHIFTL t48, TargetConstant:i8<4>
due to v8i1 only available under AVX512DQ.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D84922