Fix broken links on https://www.rtems.org/architectures/

Summary

Please highlight the value of Rtems in the architecture page:

1. All links point to a blank page We are working on content this page is intentionally left blank with an additional link to the source code. Please point to the pages in the reference documentation such as https://docs.rtems.org/branches/master/cpu-supplement/arm.html, or to the source code directly if that's the intention. Right now there is no point in consulting this architectures page.
2. Why mention "obsoleted ports" at all on this page? Can that information be moved to a page specific to a particular release, for example https://docs.rtems.org/branches/master/cpu-supplement/preface.html ?
3. What is the process for having new supported architectures and what are the future plans for the RTEMS project?