ARM: dts: add Ka-Ro tx53 devicetree

This adds support for the Ka-Ro TX53 System-On-Module.
As a baseboard is needed to operate it, only a *.dtsi and no Makefile entry.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>