ARM: dts: meson8: add the canvas module

Add the canvas module to Meson8 because it's required for the VPU
(video output) and video decoders.

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

Amlogic's vendor kernel has an explicit #define for the "DMC" register
range on Meson8m2 while there's no such #define for Meson8. However, the
canvas and memory controller registers on Meson8 are all expressed as
"0x6000 + actual offset", while Meson8m2 uses "DMC + actual offset".
Thus it's safe to assume that the DMC bus exists on both SoCs even
though the registers inside are slightly different.

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