AVX512: Change VPMOVB2M DAG lowering , use CVT2MASK node instead TRUNCATE.

AVX512: Change VPMOVB2M DAG lowering , use CVT2MASK node instead TRUNCATE.
Fix TRUNCATE lowering vector to vector i1, use LSB and not MSB.
Implement VPMOVB/W/D/Q2M intrinsic.

Differential Revision: http://reviews.llvm.org/D15675

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@256470 91177308-0d34-0410-b5e6-96231b3b80d8