ARM: DaVinci: EMAC: Clean up the fixed address offsets used for EMAC internal modules

Cleanup the way the memory regions are intialised and removes the hard-coded
offsets used for EMAC internal modules (MDIO, Control RAM, EMAC wrapper)
i.e the assumption that all modules are at fixed offset from the EMAC "base".

Also removes the hard coded values for the RAM size, number of transmit and
receive buffer descriptors, instead gets the info from the driver structure.
Signed-off-by: Chaithrika U S <chaithrika@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>