[llvm-exegesis] Disable the LBR check on AMD

https://bugs.llvm.org/show_bug.cgi?id=48918

The bug reported a hang (or very very slow runtime) on a Zen2. Unfortunately, we don't have the hardware right now to debug it and I was not able to reproduce the bug on a HSW.
Theory we've got is that the lbr-checking code could be confused on AMD.

Differential Revision: https://reviews.llvm.org/D97504