netdev/phy: Implement ieee802.3 clause 45 in mdio-octeon.c

The Octeon SMI/MDIO interfaces can do clause 45 communications, so
implement this in the driver.

Also fix some comment formatting to make it consistent and to comply
with the netdev style.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>