Add support for vhier, generating file list, module list, xml file

[Risto97]

I liked the idea of copy_rtl_files(), however I would separate vhier as a separate target and copy_rtl_files should process xml file generated from vhier.

This function also uses Generator expressions for handling function arguments, which is the proposed way of handling function arguments

[mksoc]

At the moment, I'm actually using a modified version of vhier to print a more useful output for us (https://github.com/HEP-SoC/verilog-perl), but if we parse the XML I believe we already have everything we need, even with the "stock" vhier.

We can look into modifying the Python script to parse the XML and change copy_rtl_files() accordingly.