docs: iio: add documentation for BNO055 driver

The bno055 driver is rather complex and have some oddities and not-obvious
things that worth to document (e.g. calibration files).

This patch also contains this [0] fix squashed in.

[0] https://lore.kernel.org/lkml/20220704034041.15448-1-bagasdotme@gmail.com/



Signed-off-by: Andrea Merello <andrea.merello@iit.it>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220907132205.28021-15-andrea.merello@iit.it


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