drm: omapdrm: dss: Initialize DSS internal features at probe time

The DSS internal features are derived from the platform device
compatible string which is available at probe time. Don't delay
initialization until bind time. This prepares for the merge of the two
DSS features structures that will be needed before the DSS is bound.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>