Move the DRM-backend into a new sub-directory to make it stand out from
libweston core. This facilitates splitting drm.c into more files later.
vaapi-recorder is used only by DRM-backend, move that too.
libbacklight is used only by DRM-backend and a manual test program, and is
moved as well.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
