ARM: dts: meson8b: add the canvas module

Add the canvas module to Meson8b because it's required for the VPU
(video output) and video decoders.

The canvas module is located inside the "DMC bus" (where also some of
the memory controller registers are located). The "DMC bus" itself is
part of the so-called "MMC bus".

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>