ARM: dts: sun8i: a33 Enable our display frontend

The display frontend can be used to do hardware scaling, colorspaces
conversion or to implement the buffer format output by the Cedar VPU.

Since we're starting to have some support for it in the DRM driver, let's
enable its DT node.

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