ARM: dts: sun4i: Add DRAM gates

The DRAM gates controls direct memory access for some peripherals.
These peripherals include the display pipeline, so add the required
gates to the simplefb nodes as well.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>