[AVX512] Add codegen test for the masking variant of valign

The AddedComplexity is needed just like in avx512_perm_3src.  There may be a
bug in the complexity computation...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215168 91177308-0d34-0410-b5e6-96231b3b80d8