ARM: dts: sun8i: a33: Remove unnecessary reserved memory node

While we believed that the memory for the video engine had to be kept
in the first 256 MiBs of DRAM, this is no longer true starting with the
A33 and any address can be mapped.

As a result, remove the reserved memory node and let the kernel allocate
the CMA pool wherever it sees fit.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>