drm/sun4i: Add has_channel_0 TCON quirk

Some TCONs on newer SoCs doesn't support channel 0, since they are meant
to be used only with TV or HDMI encoder.

Prepare support for them with adding has_channel_0 quirk.

Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
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/20180214200906.31509-8-jernej.skrabec@siol.net