arm64: dts: freescale: add support for solidrun solidsense-n8 board

arm64: dts: freescale: add support for solidrun solidsense-n8 board

Add support for the SolidRun SolidSense N8 Compact.

The board is designed around the i.MX8MN SoC and comes as a complete
product including enclosure and labels.

Features:
- USB-2.0 Type A connector
- 1Gbps RJ45 Ethernet with PoE
- microSD connector
- eMMC
- Cellular Modem + SIM holder
- WiFi + Bluetooth
- RS485
- CAN
- 802.15.1 radio
- supercapacitor backup power supply

This is a headless design without display.

The board includes an internal expansion connector for daughterboards
which may be described by dt addon.

The supercap is not currently described due to lack of suitable bindings.
Vendor BSP uses gpio-keys driver to trigger shutdown on power loss.

Signed-off-by: Josua Mayer <josua@solid-run.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>