drm/omap: dss: Functions to check components in the display/output list

The functions can be used to check a component (by it's of_node) if it is
part of the omapdss display or output list. If the component is found, it
means that the driver is loaded.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>