drivers: sensor: Add driver for TI INA3221

This patch adds support for the TI INA3221 current monitor.
This is the datasheet used for reference:
https://www.ti.com/lit/gpn/ina3221



Since this device has three channels, there is a custom attribute to
select which channel is to be used when getting a sample.
Measurements are done on all enabled channels.

Signed-off-by: Maximilian Deubel <maximilian.deubel@nordicsemi.no>