ARM: dts: sun8i: a83t: Add LVDS pins group

The A83T has an LVDS bus that can be connected to a panel or a bridge. Add
the pinctrl group for it.

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