iio: adc: Add TI ADS1100 and ADS1000

The ADS1100 is a 16-bit ADC (at 8 samples per second).
The ADS1000 is similar, but has a fixed data rate.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230307065535.7927-2-mike.looijmans@topic.nl


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>