[AVX512] Two new attributes in X86VectorVTInfo for subvector insert

The new attributes are NumElts and the CD8TupleForm.  This prepares the code
to enable x8 and x2 inserts.

NFC, no change in X86.td.expanded except for the new attributes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219871 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed