net: davinci_emac: Fix platform data handling and make usable for am3517

net: davinci_emac: Fix platform data handling and make usable for am3517

When booted with device tree, we may still have platform data passed
as auxdata. For am3517 this is needed for passing the interrupt_enable
and interrupt_disable callbacks that access the omap system control module
registers. These callback functions will eventually go away when we have
a separate system control module driver.

Some of the things that are currently passed as platform data we don't need
to set up as device tree properties as they are always the same on am3517.
So let's use a new compatible flag for those so we can get those from
the device tree match data.

Also note that we need to fix setting of phy_dev to NULL instead of an empty
string as the code later on uses that to find the first phy on the mdio bus.
This seems to have been caused by 5d69e0076a72 (net: davinci_emac: switch to
new mdio).

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: David S. Miller <davem@davemloft.net>