ARM: dts: sun7i-a20: Add Video Engine and reserved memory nodes

This adds nodes for the Video Engine and the associated reserved memory
for the A20. Up to 96 MiB of memory are dedicated to the CMA pool.

The VPU can only map the first 256 MiB of DRAM, so the reserved memory
pool has to be located in that area. Following Allwinner's decision in
downstream software, the last 96 MiB of the first 256 MiB of RAM are
reserved for this purpose.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>