[swss]: Generate config files for Everflow and IPinIP from minigraph
- Add Everflow DST IP to minigraph file
- Extend minigraph.py to support Everflow
- Add templates file for Everflow and IPinIP configuration
- Add config.sh for swss docker to generate config files
( All device-specific files now reside under /device directory in a <vendor-name>/<platform-string>/<hardware-SKU> directory structure in repo.
* Device-specific files are now packaged into a Debian package (sonic-device-data) and are now installed to /usr/share/sonic/device/<platform-string>/<hardware-SKU>/ directory on switch.