arm64: dts: marvell: Add Armada 98DX2530 SoC and RD-AC5X board

arm64: dts: marvell: Add Armada 98DX2530 SoC and RD-AC5X board

The 98DX2530 SoC is the Control and Management CPU integrated into
the Marvell 98DX25xx and 98DX35xx series of switch chip (internally
referred to as AlleyCat5 and AlleyCat5X).

These files have been taken from the Marvell SDK and lightly cleaned
up with the License and copyright retained.

gregory.clement: use specific cpu type: cortex-a55 instead of armv8 in
cpu nodes, armv8 being reserved for the arm virtual models that are
not meant to implement a particular CPU type.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>