OWNERS: rework security layout

We're going to be adding more ebuilds, so rework the owners layout to
allow the security team access.

BUG=b:187790077
TEST=CQ passes

Change-Id: Idf6758c94cfbc695f9dc0f1de93e0a8abd721409
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/4122809
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Allen Webb <allenwebb@google.com>
Commit-Queue: Allen Webb <allenwebb@google.com>
7 files changed