Using an external DAC for VGA output was available on sun5i. Since
some other SoCs don't have a builtin TV encoder, but might have
use for a VGA output, enable the option for the platforms that
don't have TV encoders.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>