Code style correction of cva6

[whutddk]

fix #477

Hello all, according to #477 , I have add prefixs "cva6_" to most of the RTL files, modules, and instantiation. So far, my tests only prove that the flow make fpga, which is for Genesys II is working properly. I will also test the other flow soon, because macro may block some bugs, which miss prefixs.

---

The mainly changes are as followed:

• file name, module name, instantiation name
• ariane -> cva6
• riscv_pkg -> cva6_riscv_pkg
• ariane_pkg -> cva6_pkg
• std_cache_pkg -> cva6_std_cache_pkg
• wt_cache_pkg -> cva6_wt_cache_pkg

---

The RTL codes in submodule are not modified, by the way.

[Jbalkind]

Your modifications under the openpiton/ directory will break openpiton downstream. Please submit an appropriate PR to openpiton if you are going to change those filenames and interface wires.

Edit: To be clear, such a PR to OpenPiton should not change any OpenPiton module names or macro names. Simply the module instantiations and wire names that you have modified in this PR

[whutddk]

@Jbalkind Yes I understand, and modifying the code style is a huge job and easy to make mistakes. All related repositories should be changed at the same time to avoid errors. I will try to do that soon. And only after that, we can merge the PR.