Find valid crtc for screenshot.

This change completes some of the drm structures and searches
for a valid crtc to take the screenshot from.

BUG=chromium:476791
TEST=Ran on alex.

Change-Id: I84a2c85061c2e2e897051d6cfad3211247518c03
Reviewed-on: https://chromium-review.googlesource.com/272546
Commit-Queue: Ilja Friedel <ihf@chromium.org>
Trybot-Ready: Ilja Friedel <ihf@chromium.org>
Tested-by: Ilja Friedel <ihf@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
1 file changed