misc: Updated the RELEASE-NOTES and version number

Updated the RELEASE-NOTES.md and version number for the v20.1.0.2
hotfix release.

Change-Id: Ibb6b62a36bd1f9084f7d8311ff1f94b8564dbe9b
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37435
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
3 files changed