drm/bridge: parade-ps8622: add drm_panel_bridge support

drm/bridge: parade-ps8622: add drm_panel_bridge support

Prepare the bridge driver for use in a chained setup by
replacing direct use of drm_panel with drm_panel_bridge support.

The connecter is now either created by the panel bridge or the display
driver. So all code for connector creation in this driver is no longer
relevant and thus dropped.

The connector code had some special polling handling:
    connector.polled = DRM_CONNECTOR_POLL_HPD;
    drm_helper_hpd_irq_event(ps8622->bridge.dev);

This code was most likely added to speed up detection of the connector.
If really needed then this functionality belongs somewhere else.

Note: the bridge panel will use the connector type from the panel.

v2:
  - Fix to avoid creating connector twice (Laurent)
  - Drop all connector code - defer to bridge panel
  - Use panel_bridge for local variable to align with other drivers
  - Set bridge.type to DRM_MODE_CONNECTOR_LVDS;

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
Cc: Jonas Karlman <jonas@kwiboo.se>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20200726203324.3722593-9-sam@ravnborg.org