fff-support: Add device name and firmware version to MOTD

This adds a line containing the device name and the current
firmware version to the MOTD shown after logging in via SSH, e.g.

> TP-Link TL-WR1043N/ND v2 @ jubtl9_20190320

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Fabian Bläse <fabian@blaese.de>