Add redirects to moved documentation

When moving pages around I, for whatever reason, didn't consider that this creates a bunch of stale links. The drm-misc link in MAINTAINERS being perhaps the worst one to go 404.

We could, and should, fix a lot of the now stale links, but in the mean time, use the sphinx-reredirects extension https://documatt.com/sphinx-reredirects/ to create redirects for the relocated pages.