Add RISC-V Compliance v2 check

RISC-V defines a Compliance Framework which is available in v0.2 as RISCOF.
It is still marked as beta but is now at a point where it can be utilised.
It allows for a more flexible way to check for compliance.

I hacked together a first test which runs some checks successfully. This is based on the current dv/riscv-compliance work as it will also compare the generated signatures.
It sill needs some work for an initial version.
This issue should keep track of the open points and questions.

• Implement Ibex model plugin according to riscof-plugins
  • Make it variable so different configurations of Ibex can be checked
• Can / should ibex_config.py be extended to generate a YAML specification which is needed by riscv-config which serves as an input checker for RISCOF
• Add to CI
• Choose the reference model to which Ibex is compared
• Document the usage
• Remove riscv-compliance? I am not yet sure how RISCOF is integrated into riscv-compliance as mentioned in https://github.com/riscv/riscv-compliance#issuecomment-747524231. Maybe it is only a way to run the test created in the new framework?

Documentation for reference RISCOF, riscv-config, riscv-isac

Start by reviewing the existing dv/riscv-compliance work and the first RISCOF test, then read the RISCOF, riscof-plugins, riscv-config, and riscv-isac documentation. Use ibex_config.py when assessing YAML generation, and define completion around the Ibex plugin, configurable checks, reference model, CI integration, usage documentation, and the riscv-compliance integration decision.