drm/tilcdc: Provide ddc symlink in connector sysfs directory

Use the ddc pointer 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: Jyri Sarha <jsarha@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ <b8faad34102a91698b55dfc1ce02b1a90fda5e44.1564591626.git.andrzej.p@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/ <db323a3cdfd643cef65d796e959c16a14f105920.1564591626.git.andrzej.p@collabora.com
Link: https://patchwork.freedesktop.org/patch/msgid/ <b8faad34102a91698b55dfc1ce02b1a90fda5e44.1564591626.git.andrzej.p@collabora.com