drm/rockchip: cdn-dp: add more log for video config

In order to analyze some video config failed, add some useful
printouts.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1488940077-22297-4-git-send-email-zyw@rock-chips.com