iio: adc: ti-ads1119: Add driver

The ADS1119 is a precision, 16-bit, analog-to-digital converter (ADC)
that features two differential or four single-ended inputs through a
flexible input multiplexer (MUX), rail-to-rail input
buffers, a programmable gain stage, a voltage reference, and an
oscillator.

Apart from normal single conversion, the driver also supports
continuous conversion mode using a triggered buffer. However, in this
mode only one channel can be scanned at a time.

Datasheet: https://www.ti.com/lit/gpn/ads1119


Signed-off-by: João Paulo Gonçalves <joao.goncalves@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://patch.msgid.link/20240617183905.4685-1-francesco@dolcini.it


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