Add unblocked_terms.txt and PRESUBMIT.cfg

The EDK2 project is not controlled or owned by ChromeOS.  Unblock the
blocked terms so that commits can go in and quiet the prechecks.

BUG=None
TEST=Commit change

Change-Id: I498adc11eb7139efd6641f70ab22e2b25eb0e6e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/edk2/+/3206271
Reviewed-by: Karthikeyan Ramasubramanian <kramasub@chromium.org>
Commit-Queue: Martin Roth <martinroth@google.com>
Tested-by: Martin Roth <martinroth@google.com>
Auto-Submit: Martin Roth <martinroth@google.com>