Updating Ibex simple system ISA string
The Ibex SS method SimpleSystem::GetIsaString currently returns an ISA string that contains Xbitmanip. We want to eventually move that to the proper bitmanip subextension names.
On the simulation side, this needed some Spike support, which is merged in https://github.com/riscv-software-src/riscv-isa-sim/commit/c2f30c33304c96917bdb0ab7e2d4d6a2d71d1d25. Note that this appears in the ibex-cosim-v0.2 tag that we're moving to as a dependency Real Soon Now.
I believe that Spike support is fully integrated so Ibex SS method should now be correct. @luismarques - could you comment on if you believe this is still an issue or if we can close this?