omap: add mdio platform devices

This patch adds mdio platform devices on SoCs that have the necessary
hardware.  Clock lookup entries (aliases) have also been added, so that the
MDIO and EMAC drivers can independently enable/disable a shared underlying
clock.  Further, the EMAC MMR region has been split down into separate MDIO
and EMAC regions.

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>