ARM: dts: sun8i: r40: Disable TCONs by default.

R40 has 4 TCONs, but only 2 of them can receive some kind of output at
the same time. Let's disable them by default, so only those which are
really connected on board can be enabled in board dts file.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>