ARM: dts: sun7i: Add LVDS panel support on A20

Define pins for LVDS channels 0 and 1, configure reset line for tcon0 and
provide sample LVDS panel, connected to tcon0.

Signed-off-by: Andrey Lebedev <andrey@lebedev.lt>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>