kirkwood: use real model names for Linksys devices

kirkwood: use real model names for Linksys devices

This replaces the internal device names "Audi" and "Viper" with the
real model names, which a user would look for. This makes the
Linksys devices on this target consistent with the names recently
changed for mvebu based on the same idea.

As a consequence, the "viper" device definition is split into two
separate definitions with the correct names for both real models.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>