Revert "drm/panel: Add device_link from panel device to DRM device"

This reverts commit 0c08754b59da5557532d946599854e6df28edc22.

commit 0c08754b59da
("drm/panel: Add device_link from panel device to DRM device")
creates a circular dependency under these circumstances:

1. The panel depends on dsi-host because it is MIPI-DSI child
device.
2. dsi-host depends on the drm parent device (connector->dev->dev)
this should be allowed.
3. drm parent dev (connector->dev->dev) depends on the panel
after this patch.

This makes the dependency circular and while it appears it
does not affect any in-tree drivers (they do not seem to have
dsi hosts depending on the same parent device) this does not
seem right.

As noted in a response from Andrzej Hajda, the intent is
likely to make the panel dependent on the DRM device
(connector->dev) not its parent. But we have no way of
doing that since the DRM device doesn't contain any
struct device on its own (arguably it should).

Revert this until a proper approach is figured out.

Cc: Jyri Sarha <[e-mail]>
Cc: Eric Anholt <[e-mail]>
Cc: Andrzej Hajda <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
Signed-off-by: Sean Paul <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_panel.c

···
 #include <linux/err.h>
 #include <linux/module.h>
 
-#include <drm/drm_device.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_panel.h>
 
···
 	if (panel->connector)
 		return -EBUSY;
 
-	panel->link = device_link_add(connector->dev->dev, panel->dev, 0);
-	if (!panel->link) {
-		dev_err(panel->dev, "failed to link panel to %s\n",
-			dev_name(connector->dev->dev));
-		return -EINVAL;
-	}
-
 	panel->connector = connector;
 	panel->drm = connector->dev;
 
···
  */
 int drm_panel_detach(struct drm_panel *panel)
 {
-	device_link_del(panel->link);
-
 	panel->connector = NULL;
 	panel->drm = NULL;
 

include/drm/drm_panel.h

···
 	struct drm_device *drm;
 	struct drm_connector *connector;
 	struct device *dev;
-	struct device_link *link;
 
 	const struct drm_panel_funcs *funcs;