test_platform: Add config fields to control SSP base image

BUG=chromium:1103904
TEST=./generate.sh

Change-Id: I4a1d62fa4f89d595796b13cb191de9952892ea85
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/proto/+/2309191
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
4 files changed