drivers:adc:ad7768-1: Add support for ADAQ776x-1 Family

[adiceline]

Pull Request Description

This PR adds driver support for the ADAQ776x-1 ADC with IIO attributes and example usage.

PR Type

• [ ] Bug fix (change that fixes an issue)
• [X] New feature (change that adds new functionality)
• [ ] Breaking change (has dependencies in other repos or will cause CI to fail)

PR Checklist

• [X] I have followed the Coding style guidelines
• [X] I have complied with the Submission Checklist
• [X] I have performed a self-review of the changes
• [X] I have commented my code, at least hard-to-understand parts
• [X] I have build all projects affected by the changes in this PR
• [X] I have tested in hardware affected projects, at the relevant boards
• [X] I have signed off all commits from this PR
• [X] I have updated the documentation (wiki pages, ReadMe etc), if applies

[CLAassistant]

All committers have signed the CLA.

[buha]

also, typo in 1st commit title