iio: accel: Add support for the Bosch-Sensortec BMI088

The BMI088 is a combined module with both accelerometer and gyroscope.
This adds the accelerometer driver support for the SPI interface.
The gyroscope part is already supported by the BMG160 driver.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210125150732.23873-2-mike.looijmans@topic.nl


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>