ARM: dts: imx7-colibri: fix muxing of usbc_det pin

USB_C_DET pin shouldn't be in ethernet group.

Creating a separate group allows one to use this pin
as an USB ID pin.

Fixes: b326629f ("ARM: dts: imx7: add Toradex Colibri iMX7S/iMX7D suppor")
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>