drm/sun4i: Don't check for LVDS and RGB when TCON has only ch1

LVDS and RGB interfaces are always connected to TCONs which have channel
0. It doesn't make sense to try to init them on TV TCONs.

Add a check if TCON has channel 0 before trying to init LVDS or RGB
interface.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180625120304.7543-12-jernej.skrabec@siol.net