[X86] Explicitly mark unsupported classes in scheduling models.

Summary: In preparation for D47721. HSW and SNB still define unsupported
classes as they are used by KNL and generic models respectively.

Reviewers: RKSimon

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47763

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334389 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed