dt-bindings: arm: fsl: Add DHCOM PicoITX and DHCOM DRC02 boards

Add DH electronics DHCOM PicoITX and DHCOM DRC02 boards. The DHCOM DRC02
device can only house a SOM with iMX6S and not with iMX6DL, due to some
thermal design consideration. But for compatible fsl,imx6dl is chosen,
because fsl,imx6s isn't available, the iMX6S is basically a iMX6DL with
one CPU core disabled and therefore the kernel discerns the iMX6S/iMX6DL
automatically.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Cc: robh+dt@kernel.org
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: kernel@dh-electronics.com
Cc: Fabio Estevam <festevam@denx.de>
To: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>