ARM: dts: imx6ul: Add DTS for ConnectCore 6UL SBC Express

The ConnectCore 6UL Single Board Computer (SBC) Express contains the
ConnectCore 6UL System-On-Module.

Its hardware specifications are:

* 256MB DDR3 memory
* 256MB NAND flash
* Single Ethernet
* USB Host and USB-OTG
* MicroSD external storage
* Groove connectors and Raspberry Pi Hat compatible expansion header

Signed-off-by: Alex Gonzalez <alex.gonzalez@digi.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>