ARM: dts: imx6qdl-dhcom: Add DHCOM based PicoITX board

Add DT for DH PicoITX unit, which is a bare-bones carrier board for
the DHCOM. The board has ethernet port, USB, CAN, LEDs and a custom
board-to-board expansion connector.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: kernel@dh-electronics.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>