compositor-drm: Track unused connectors and CRTCs

compositor-drm: Track unused connectors and CRTCs

Rather than a more piecemeal approach at backend creation, explicitly
track connectors and CRTCs we do not intend to use, so we can ensure
they are disabled where appropriate.

When we have an updated list of connector and CRTC IDs, we add any which
are not owned by an enabled drm_output to the list. We remove them from
the list when drm_output_repaint() is called for that output, and re-add
them when the output is disabled or destroyed.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>