iio/gyro/bmg160: Add support for BMI088 chip

The BMI088 is pin-compatible with the BMI055, and provides
both gyro and accel functions. The gyro part is similar to
the BMI055 and this adds the chip to the list of supported
devices for the gyro part.

The accel part of the chip is not compatible with anything
existing already.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>