CRIS: Update main Kbuild makefile.

- Remove old and non-generic targets, use generic ones instead.
- Add sub-arch as mach-fs or mach-a3 for EtraxFS and Artpec-3 respectively.
- Add links to sub-arch directories, and erase before trying to create them.
- Include from sub-arch specific include directory "mach".
- Add files to be cleaned in CLEAN_FILES instead of as archclean target.