ARM: dts: imx: add Boundary Devices Nitrogen6_SoloX board

Based on i.MX6 SoloX with 1GB of RAM.

https://boundarydevices.com/product/nit6_solox-imx6/



Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>