net: stmmac: Add ip version to dts bindings

Because there are multiple variants to the stmmac/dwmac driver, the
dts bindings should be updated to include version of the IP used.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>