[X86] Add DAG combine to promote vXi1 result of a vXi8/vXi16 setcc when we have AVX51...

[X86] Add DAG combine to promote vXi1 result of a vXi8/vXi16 setcc when we have AVX512 but not BWI.

This avoids having the result type stick around until lowering where we have to extend the setcc and insert a truncate. If we get the types converted early we can do more to optimize it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322432 91177308-0d34-0410-b5e6-96231b3b80d8