arm64: dts: add description for solidrun cn9131 solidwan board

arm64: dts: add description for solidrun cn9131 solidwan board

Add description for the SolidRun CN9131 SolidWAN, based on CN9130 SoM
with an extra communication  processor on the carrier board.

This board differentiates itself from CN9130 Clearfog by providing
additional SoC native network interfaces and pci buses:
2x 10Gbps SFP+
4x 1Gbps RJ45
1x miniPCI-E
1x m.2 b-key with sata, usb-2.0 and usb-3.0
1x m.2 m-key with pcie and usb-2.0
1x m.2 b-key with pcie, usb-2.0, usb-3.0 and 2x sim slots
1x mpcie with pcie only
2x type-a usb-2.0/3.0

Signed-off-by: Josua Mayer <josua@solid-run.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>