ARM: dts: imx6dql-nitrogen6x: add touchscreen support

This patch adds the different touchscreens that can be connected using
the displays available for this board.
http://boundarydevices.com/product-category/displays/



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