ozone: Enable vulkan by default

Vulkan is enabled by default on Linux desktop (X11) builds. Enable it on
ozone as well to make sure we have build coverage.

Bug: 861853
Test: compile
Change-Id: I7c15e365b2a4cfc7160847457ce9bf46a3f12f1e
Reviewed-on: https://chromium-review.googlesource.com/1229233
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592451}
2 files changed