[X86][Sched] Add zero idiom sched data to the SNB model.

[X86][Sched] Add zero idiom sched data to the SNB model.

Summary:
On SNB, renamer-based zeroing does not work for:
 - 16 and 8-bit GPRs[1].
 - MMX [2].
 - ANDN variants [3]

[1] echo 'sub %ax, %ax' | /tmp/llvm-exegesis -mode=uops -snippets-file=-
[2] echo 'pxor %mm0, %mm0' | /tmp/llvm-exegesis -mode=uops -snippets-file=-
[3] echo 'andnps %xmm0, %xmm0' | /tmp/llvm-exegesis -mode=uops -snippets-file=-

Reviewers: RKSimon, andreadb

Subscribers: gbedwell, craig.topper, llvm-commits

Differential Revision: https://reviews.llvm.org/D52358

llvm-svn: 342736