libchromeos: Use gbm platform for zako_freon board

BUG=chromium:428125
TEST=build zako_freon board, verify WebGL works

Change-Id: Ieaf2fc2aee96d6aa1b6ed8918dab034a69af72e7
Reviewed-on: https://chromium-review.googlesource.com/229652
Commit-Queue: Haixia Shi <hshi@chromium.org>
Tested-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Haixia Shi <hshi@chromium.org>
1 file changed