drm: omapdrm: dpi: Remove dpi_data port_initialized field

The dpi_data structure port_initialized field is used to check in the
cleanup path whether the DPI has been initialized. This can be performed
through the associated device_node data field instead. Remove the
port_initialized field.

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>