dt-bindings: arm: fsl: Add devicetree binding for Eckelmann ci4x10

Add devicetree binding for Eckelmann's ci4x10 board which is powered by
an i.MX6DL SoC.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>