The USB connector should not be placed under the dwc3 node.

Move the USB connector out of the SoC level and use port to describe
the connection to the dwc3 controller.

This fixes the following dt-schema warning:

imx8mp-tqma8mpql-mba8mpxl.dtb: usb@38100000: Unevaluated properties are not allowed ('connector' was unexpected)
	from schema $id: http://devicetree.org/schemas/usb/snps,dwc3.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>