drm/exynos: Provide ddc symlink in connector's sysfs

Switch to using the ddc provided by the generic connector.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Inki Dae <inki.dae@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ <613c1c09ff7db5be60ef86f930b45b3f56b4838d.1564591626.git.andrzej.p@collabora.com