Change target name in makefile, "bin" clashes with xcommon
Make code more readable

- Restructure: move definitions to headers;
- Rename files, vars and functions to better reflect their purpose;
- Change constants to definitions;
- Comment some code parts.
Update XN file for XTAG2

- Handle "core" -> "tile" rename to make it compile in toolchain v 13;
- Add USB port names, looks like it is required by more recent XUD
  library.
Minor change
Add make configs for XTAG-2 and startKIT