iio: light: Add driver for IDT ZOPT2201 ambient light and UVB sensor

Driver for 20-bit ALS and UV B sensor with I2C interface exposing
the following API:
  in_uvindex_input
  in_illuminance_raw
  in_illuminance_scale
  in_illuminance_scale_available
  in_intensity_uv_raw
  in_intensity_uv_scale
  in_intensity_uv_scale_available
  integration_time
  integration_time_available

Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>