net: davinci_emac: switch to new mdio

This patch switches the emac implementation over to the newly separated
MDIO driver.

With this, the mdio bus frequency defaults to a safe 2.2MHz.  Boards may
optionally specify a bus frequency via platform data.

The phy identification scheme has been modified to use a phy bus id instead
of a mask.  This largely serves to eliminate the "phy search" code in emac
init.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
Acked-by: David S. Miller <davem@davemloft.net>
Tested-by: Michael Williamson <michael.williamson@criticallink.com>
Tested-by: Caglar Akyuz <caglarakyuz@gmail.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>