mvebu: add support for SolidRun ClearFog Pro

The SolidRun ClearFog Pro is a router based on the SolidRun CN9130 SOM.

Specs:
 - SoC: Quad-Core Cortex-A72 CN9130 SoC
 - RAM: 4GiB DDR4
 - Serial: Micro-USB port on front (FT232R, 115200 8n1)
 - Storage: 8GiB eMMC, microSD card slot, 8MiB SPI NOR flash
 - Ethernet: 7x GbE (1 port dedicated on SoC, 6 port switch with single GbE CPU port)
 - SFP: 1x SFP+
 - USB: 1x USB-A 3.1 Gen 1
 - PCIe: 2x mini PCIe (one slot with USB and SIM card socket)
 - SATA: 1x M.2 Key-B

In addition to the usual connectivity options this device also features
an internal mikroBUS expansion connector.

SATA is currently untested due to lack of a suitable M.2 SSD.

Installation
============

1. Write sdcard sysupgrade image to microSD card using dd or similar
2. Insert microSD card into router and apply power
3. Device boots into OpenWRT
4. (optional) dd sysupgrade image to /dev/mmcblk0 to install to eMMC

Signed-off-by: Tobias Schramm <tobias@t-sys.eu>