drm/sun4i: cec: Enable back CEC-pin framework

Now that the cec-pin framework has been merged, we can remove the safeguard
that were preventing the CEC part of the sun4i HDMI driver and actually
start to use it.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>