iio: accel: adxl380: add support for ADXL318 and ADXL319

iio: accel: adxl380: add support for ADXL318 and ADXL319

The ADXL318 and ADXL319 are low noise density, low power, 3-axis
accelerometers based on ADXL380 and ADXL382, respectively. The main
difference between the new parts and the existing ones are the absence
of interrupts and events like tap detection, activity/inactivity, and
free-fall detection.

Other differences in the new parts are fewer power modes, basically
allowing only idle and measurement modes, and the removal of the 12-bit
SAR ADC path for the 3-axis signals (known as lower signal chain),
being excluisive for the temperature sensor in the ADXL318/319.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>