The R8 is very close to the A13, but it still has a few differences,
notably a composite output, which the A13 lacks.

Add a DTSI based on the A13's to hold those differences.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>