[X86] Fix skylake server scheduling info.

Summary:
This fixes most of the scheduling info for SKX vector operations.
I had to split a lot of the YMM/ZMM classes into separate classes for YMM and ZMM.

The before/after llvm-exegesis analysis are in the phabricator diff.

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47721

llvm-svn: 334407