arm: mvebu: Support for 98DX25xx/98DX35xx SoC

Add support for the Allecat5/Alleycat5X SoC. These are L3 switches with
an integrated CPU (referred to as the CnM block in Marvell's
documentation). These have dual ARMv8.2 CPUs (Cortex-A55). This support
has been ported from Marvell's SDK which is based on a much older
version of U-Boot.

Signed-off-by: Chris Packham <judge.packham@gmail.com>