iio: accel: adxl345: add calibration offset support
The ADXL345 provides the offset adjustment registers for each axis.
This adds the iio channel information for the calibraion offsets with
that feature.
Cc: Eva Rachel Retuya <eraretuya@gmail.com> Cc: Andy Shevchenko <andy.shevchenko@gmail.com> Cc: Jonathan Cameron <jic23@kernel.org> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>