Some of the init functions unilaterally enable set auto cross over
without using the helper. Make use of the helper, and respect the
phydev MDI configuration.

Clean up the #define used while setting polarity, and the other
functions of the bits in the register.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>