arm64: dts: imx8mn-var-som-symphony: Describe the USB-C connector

Describe the PTN5150 USB-C connector to improve the devicetree description
and fix the following dt-schema warning:

imx8mn-var-som-symphony.dtb: typec@3d: 'port' does not match any of the regexes: 'pinctrl-[0-9]+'
	from schema $id: http://devicetree.org/schemas/extcon/extcon-ptn5150.yaml#

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>