input: sensors: register wake-up interface for MPU6050

Sensor class enable_wakeup interface is to provide user space
interface to configure sensor to work on wake-up mode. This change
add MPU6050 wake-up callback function and register it to sensor
class.

Change-Id: If84ec2cd008c8cd1161b94de227aa1a3b45621a6
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>