iio: magnetometer: si7210: add driver for Si7210

iio: magnetometer: si7210: add driver for Si7210

Silicon Labs Si7210 is an I2C Hall effect magnetic position and
temperature sensor. The driver supports the following functionalities:
* reading the temperature measurements
* reading the magnetic field measurements in a single-shot mode
* choosing the magnetic field measurement scale (20 or 200 mT)

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Antoni Pokusinski <apokusinski01@gmail.com>
Link: https://patch.msgid.link/20250120215620.39766-3-apokusinski01@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>