Document tests or software that are fixed to specific commit versions and need periodic update

During update https://github.com/kernelci/kernelci-core/pull/2446 i discovered that we are using very old commit for libhugetlbfs sources, and there is few other places, where some fixed firmware commit set. And, sure, for example updating buildroot images and etc.
We need to list such places, give reason why it is frozen on specific commit, why and when need to be periodically updated.

Start with the update described in pull request 2446, then inspect the repository locations for libhugetlbfs sources, fixed firmware commits, and Buildroot images. Done means producing a list of each frozen revision with its reason, plus when and why it should be revisited.

Written by the indexing model from the issue text.