ARM: dts: colibri-imx6ull: Enable dual-role switching

The Colibri standard provides a GPIO called USBC_DET to switch from
USB Host to USB Device and back. Make use of this GPIO by adding it
with usb-connector framework.

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