[ozone/wayland/drm] Place OverlayPlane and ScanoutBuffer into shared place.

This CL is a part of Wayland gpu/ui split effort, which fixes the
Ozone/Wayland and mades it functional when the gpu service is running
out of the browser process.

The patch does not bring any functionality changes, but rather
prepares Ozone/Wayland for a dmabuf based approach, which uses ozone/drm code,
to be landed in the upstream.

In particular, overlay_plane.cc/h and scanout_buffer.h are
moved into a common folder in the ui/ozone/common/linux.
These are only compiled for wayland (downstream now) and drm backends,
and does not bring any additional load on other backends.

Bug: 820047
Change-Id: I1268eeb38e710e9a1c335def08fa94edf103095f
Reviewed-on: https://chromium-review.googlesource.com/1071928
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562465}
26 files changed