drm: omapdrm: dss: Select features based on compatible string

Use the compatible string instead of the OMAP SoC revision to determine
device features. The various OMAP3-based SoCs can't be told apart using
the compatible string, use soc_device_match() to tell them apart.

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