ARM: dts: sun9i: cubieboard4: Enable VGA display output

The Cubieboard4 has a dumb VGA DAC connected to the output of LCD0,
providing VGA output through the onboard VGA connector. The DDC lines
are connected to i2c3.

The VGA DAC is a GM7123, which is compatible with Analog Devices'
ADV7123, except it only takes 3.3V power, and has a lower standby power
consumption. The datasheet found online lists "Chengdu GoldTel Electronical
Technology Co., Ltd." as its designer. The company changed its name in
2014 to "Chengdu Corpro Technology Co., Ltd.". Their website lists similar
ICs, but not actually the GM7123.

Enable the display pipeline with the VGA DAC and connector, and i2c3
for DDC.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>