drm: Fix tiled mode detection

The TILE property is present on all connectors which are DisplayPort MST (Multi-Stream) outputs, independent if they are connected to a tiled display are not.

Starting with the 5.2 kernel, it is actually present on almost all outputs.

Rather then just checking if the property is present, check that if it is present it has a valid (non zero) blob-id assigned to it, this fixes us mis-identifying DP MST outputs as always being tiled.

Which in turn fixes us failing to pick the preferred mode on these outputs.

Signed-off-by: Hans de Goede hdegoede@redhat.com