Adding ad7386/7/8 (16/14/12 bits) unsigned, dual simultaneous sampling, single-ended compatible parts, and the corresponding ad7386-4/7-4/8-4 4 channels. These parts have a 2:1 multiplexer in front of each ADC. They also include additional configuration registers that allow for either manual selection or automatic switching (sequencer mode), of the multiplexer inputs. This commit focus on integrating manual selection. Sequencer mode will be implemented later.
