Enable these devices using the VOPL video output device. We explicitly
disable VOPB in the device tree to avoid it taking over. Since this device
has an LCD display this comes up by default. If the display fails for some
reason then it will attempt to use HDMI. It is possible to force it to fail
(and thus fall back to HDMI) by puting 'return -EPERM' at the top of
rk_edp_probe(). For now there is no easy way to select between the two.

Signed-off-by: Simon Glass <sjg@chromium.org>