net: Drop dm.h header file in eth_phy.h

This header file should not be included in other header files. Remove it
and use a forward declaration instead.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/eth_phy.h

@@ -6,9 +6,10 @@
 #ifndef _eth_phy_h_
 #define _eth_phy_h_
 
-#include <dm.h>
 #include <phy.h>
 
+struct udevice;
+
 int eth_phy_binds_nodes(struct udevice *eth_dev);
 int eth_phy_set_mdio_bus(struct udevice *eth_dev, struct mii_dev *mdio_bus);
 struct mii_dev *eth_phy_get_mdio_bus(struct udevice *eth_dev);