staging: octeon-usb: use a single .h file

Merge USBC and USBN register definitions into a single header
file. Although all HW definitions are purely internal to the driver,
it's better to keep them separate due to the large size of the file.

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