drm/omap: dss: Remove display ordering from dss/display.c

As ordering of the dss_devices based on DT aliases is now implemented in
omap_drm.c, there is no need to do the ordering in dss/display.c
anymore.

At the same time remove the alias member of the omap_dss_device struct
since it is no longer needed. The only place it was used is in the
omapdss_register_display() function.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>