Older version of this patch series reported writeback as disconnected
to avoid confusing userspace not aware of writeback connectors.
However, the version that got merged uses a special cap
(DRM_CLIENT_CAP_WRITEBACK_CONNECTORS) for this purpose.

This helps us avoid some special handling of writeback connector
in drm_helper_probe_single_connector_modes, see [1].

https://lists.freedesktop.org/archives/dri-devel/2018-July/183144.htmlSigned-off-by: NAlexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Reviewed-by: NSean Paul <seanpaul@chromium.org>
Signed-off-by: NLiviu Dudau <liviu.dudau@arm.com>