Invensense: add tuna variants

Commit 424ca7d41df7b1ea0df51c90d6cb84ef5800ef80 made building invensense sensors opt-in.
Since the Galaxy Nexus uses the variant names (maguro, toro, toroplus) instead of tuna,
this commit is needed to be able to build sensors.

Change-Id: Ia2d554f70af319fb350bfa2915cc43eac224837a