ARM: sun5i: r8: Add display blocks to the DTSI

The TCON, tv-encoder and display engine backends and frontends are combined
to create our display pipeline.

Add them to the R8 DTSI. It's supposed to be perfectly compatible with the
A10s and A13, but since we haven't tested it on them yet, it's safer to
just enable it on the R8. Eventually, it should be moved to sun5i.dtsi

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>