drivers: platform: maxim: add uart_stdio for max32670

[jsanbuen]

Pull Request Description

This PR is to have the maxim_uart_stdio available for max32670 platform. Upon inspection, the same file is used for all maxim platforms and so the same file is used for max32670.

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 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

[jsanbuen]

changelog: -added commit message