staging: octeon-usb: refactor usbn block init

Move one-time state data structure initialization out of
cvmx_usb_initialize().

This enables to re-initialize USBN HW block without messing
up data structures.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>