ARM: dts: imx6qdl-wandboard: enable USB OTG

Enable USB OTG (dual-role) on the Wandboard.
Note, that the USB_OTG_VBUS current is quite limited due to a 22R resistor
in the power line. Hence, the overcurrent signal of 1A will never be
triggered on this board.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>