iio: imu: st_lsm6dsx: move bdu/boot and reset register info in hw_settings

Move bdu, boot and reset register definitions in hw_settings register
map since not all supported sensors (e.g lsm9ds1) rely on the same
definitions

Fixes: 52f4b1f1 ("iio: imu: st_lsm6dsx: add support for accel/gyro unit of lsm9ds1")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>