The Opteron A1100 processor that AMD was using for its ARM based server lines are not using any AMD In-House custom designed ARM cores they use the Arm Holdings Reference Design A57 cores and that's all for that SKU!

AMD did have Jim Keller, at the same time that Keller/His team where working on the Zen x86 core, also working on a Keller/Arm K12 team project for an AMD custom ARM K12 Core where that Arm core was essentially using the same design ethos as Zen but that the K12 custom core was engineered to Decode and Execute the ARMv8A ISA.

But AMD's K12 custom ARM core project was mothballed and that project placed on the back burners in favor of x86 based Zen. AMD still has the Verilog(Blueprints) for K12 as Keller/K12 Team where far enough along with that for that design to be considered completed.