iox128a1u.h: Update ADC bit definitions and channel structs

[lmorrisonnautel]

Some bit names disagreed with their counterparts in the datasheet. In other cases, enums were cut short causing entire modes of operation to be completely omitted.

The ADC_CH_t struct was missing the SCAN byte, which led the entire ADC_t struct to be misaligned with the actual locations of latter registers in memory.