ARM: dts: mvebu: Add device tree for 98DX3236 SoCs

The Marvell 98DX3236, 98DX3336, 98DX4521 and variants are switch ASICs
with integrated CPUs. They are similar to the Armada XP SoCs but have
different I/O interfaces.

[gregory.clement@free-electrons.com: fix topic]
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>