input: sensors: report accurate timestamp for mpu6050

Associate accurate sensor event generation time to Accel
and Gyro data samples.Algorithms using Accel and Gyro data
need very accurate event generation timestamps.

Change-Id: Ie07c66bb986ab52ed812d3b6ddc93674db1b414e
Signed-off-by: Ananda Kishore <kananda@codeaurora.org>