iio: imu: inv_mpu6050: fix data polling interface

When reading data with the polling interface, we need to wait
at 1 sampling period to have a sample.
For gyroscope and magnetometer, we need to wait for 2 periods
before having a correct sample.

Not suitable for stable or backporting.

Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: imu: inv_mpu6050: rewrite power and engine management

Rewrite clock management to use automatic clock switching
present since MPU6500.
Sensors engine management can now turn on or off a batch of
sensors which simplifies usage a lot.
Temperature sensor is now turned on/off depending on usage.

Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

iio: imu: inv_mpu6050: add MPU925x magnetometer support

Add support of driving MPU9250 magnetometer connected on i2c
auxiliary bus using the MPU i2c master.

Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>