arm64: dts: colibri-imx8x: Disable touchscreen by default

Do not enable the touchscreen. By default it is not used but should be
kept to enable it from a file that includes imx8x-colibri.dtsi.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>