omap: cleanup unused davinci mdio arch code

This patch removes davinci architecture code that has now been rendered
useless by the previous patches in the MDIO separation series.

Signed-off-by: Cyril Chemparathy <cyril@ti.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>