kmssink: fallback to universal planes if no overlay plane is found

kmssink: fallback to universal planes if no overlay plane is found

Without setting the DRM_CLIENT_CAP_UNIVERSAL_PLANES capability bit, only
overlay planes are made available for compatibility with legacy clients.

But if a CRTC doesn't have an overlay plane associated, then kmssink is
not able to find a plane for the CRTC and the pipeline will fail, i.e:

ERROR                kmssink gstkmssink.c:482:gst_kms_sink_start:<kmssink0> Could not find a plane for crtc

If no overlay planes were found for a given CRTC, fallback to universal
planes so DRM will also return primary planes that can be used instead.

https://bugzilla.gnome.org/show_bug.cgi?id=768183

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>