Introduce rocket chip CI in scala

[ZenithalHourlyRate]

Rocket chip uses a Makefile-based CI test and it uses old rocket-tools as the toolchain, which is hard to bootstrap, understand, upgrade and extend.

Playground instead uses the latest toolchain from arch and nix. Yet, the binaries from riscv-tests can not be compiled by clang. It is observed that we need rocket-tools because we need the binaries from riscv-tests. So instead of submoduling the whole riscv-gnu-toolchain then compiling riscv-tests from source, we can compile it in another repo (with the binary release from riscv-gnu-toolchain) and only download the artifacts in playground, which is simpler and easier to maintain/bootstrap.

The key rationale is that this is a hardware repo so those tools should not be submoduled.

This supersedes #37

TODO

• [ ] openocd
  • Actually, the latest openocd works, but a patch to rocket-chip is needed.
  • Also we still need to submodule riscv-tests for its debug/gdbserver.py
• [x] riscv-tests binaries
  • [ ] Migrate binary release flow ZenithalHourlyRate/riscv-tests-release to chipsalliance
• [ ] other buckets like scalafix
• [ ] Separate into multiple buckets in github actions

[sequencer]

already did in rc