arm64: dts: colibri-imx8x: Add pinctrl group for hdmi hpd

The colibri imx8x contains a dedicated gpio meant for HDMI
hot-plug-detect. Add a pinctrl group to make this usable.

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