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

This reverts commit 0c08754b.

commit 0c08754b


("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 <jsarha@ti.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180927124130.9102-1-linus.walleij@linaro.org