input: sensors: add sensor class support for MPU6050

Sensor class interface is required for sensor HAL to
discover the sensor. This change creates sensor class
interface for INVENSENSE MPU6050 accelerometer +
gyroscope sensor combo.

CRs-fixed: 655796
Change-Id: Iec9e5cd7601b5a8a29ce5c1c267d63548afa2491
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>