media-libs/mesa: Add egl platform drm with USE=drm.

BUG=chromium:837073
TEST=xwayland with virtio-gpu.

Change-Id: I3b821b2227af00dc1a87479edaa373414643cb08
Reviewed-on: https://chromium-review.googlesource.com/1244066
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Riley <davidriley@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
3 files changed