[Doc] Migrate obsolete IPs: axi_ad9144 & axi_ad9371

[cristianmihaipopa]

PR Description

Migrate documentation for AXI IPs which are not maintained anymore from wiki to GitHub pages. This PR contains:

• two new pages (axi_ad9144 & axi_ad9371)
• new sections, in library/index.rst called 'Obsolete IPs' and in projects/index.rst called 'Obsolete Projects'

PR Type

• [ ] Bug fix (change that fixes an issue)
• [ ] 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 code style guidelines
• [x] I have performed a self-review of changes
• [ ] I have compiled all hdl projects and libraries affected by this PR
• [ ] I have tested in hardware affected projects, at least on relevant boards
• [ ] I have commented my code, at least hard-to-understand parts
• [x] I have signed off all commits from this PR
• [x] I have updated the documentation (wiki pages, ReadMe files, Copyright etc)
• [ ] I have not introduced new Warnings/Critical Warnings on compilation
• [ ] I have added new hdl testbenches or updated existing ones