staging: octeon-ethernet: move cvm_oct_xaui_open()

cvm_oct_xaui_open() is trivial and does not need a dedicated file.
Move it to the main file.

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