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
Merge "sensorservice: Add legacy sensors fusion." into cm-10.1
Merge branch 'cm-10.1' of github.com:CyanogenMod/android_frameworks_native into cm-10.1