net: mscc: ocelot: expose ocelot_pll5_init routine

Ocelot chips have an internal PLL that must be used when communicating
through external phys. Expose the init routine, so it can be used by other
drivers.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Signed-off-by: David S. Miller <davem@davemloft.net>