drm/omap: Don't call EDID read operation recursively

Instead of calling the EDID read operation (.read_edid()) recursively
from the display device back to the first device that provides EDID read
support, iterate over the devices manually in the DRM connector code.
This moves the complexity to a single central location and simplifies
the logic in omap_dss_device drivers.

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>