Developers with testing rigs having multiple graphics cards plugged in
often want to test things on a specific card. We have ways to choose a
card through seat assignments, but configuring that run by run is
awkward.
Add a command line option for opening a specific DRM device.
v2: call it --drm-device instead of --device
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Daniel Stone <daniels@collabora.com>