samples: adc_dt: adding silabs xg24_dk2601b

[silabs-agostonk]

This pull request adds support for xg24_dk2601b to the adc_dt sample app.
Measuring four channels:

• ch0: AVDD
• ch1: button0 on GPIO port B2 pin
• ch2: button1 on GPIO port B3 pin
• ch3: U.FL connector on AIN0 pin

[github-actions]

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[JarmouniA]

What is the added value of building this in CI in addition to xg24_rb4187c?

[silabs-agostonk]

Thank you to point it out, it doesn't need testing and I will remove it from here.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[kartben]

@silabs-agostonk this needs rebasing