[X86] AMD Znver2 (Rome) Scheduler enablement

The patch gives out the details of the znver2 scheduler model.
There are few improvements with respect to execution units, latencies and
throughput when compared with znver1.
The tests that were present for znver1 for llvm-mca tool were replicated.
The latencies, execution units, timeline and throughput information are updated for znver2.

Reviewers: craig.topper, Simon Pilgrim

Differential Revision: https://reviews.llvm.org/D66088