In preparation for a new robot which needs the
OTG port as host.

This moves the OTG device registration into board
initialisation.
Signed-off-by: NPhilippe Rétornaz <philippe.retornaz@epfl.ch>
Acked-by: NValentin Longchamp <valentin.longchamp@epfl.ch>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>