DisplayDevice: initialize mDisplayToken correctly

mDisplayToken should be initialized by displayToken.

Change-Id: I0a5fec1f1732200a32d10b1575239dceffe6dee4
sensorservice: Add legacy sensors fusion.

This change allows devices with accelerometer & magnetometer but
without gyroscope to still get virtual sensors such as Gravity,
Linear Acceleration and Rotation Vector.

Change-Id: Ibb90b70845c766ab52c843557446e34649a7d6d9