Added swarming dimensions to fuchsia-fyi-arm64-rel.

Added dimensions so that fuchsia-fyi-arm64-rel will run on bots with these dimensions.

Bug: 968819
Change-Id: Iea1295e0d691d631031e497425a0d9e9b3ec0a52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1710201
Commit-Queue: Karen Qian <karenqian@google.com>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#679640}