net: Drop dm.h header file from phy.h

This header file should not be included in other header files. Remove it
and use other headers and C inclusions instead.

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

include/phy_interface.h

@@ -10,6 +10,8 @@
 #ifndef _PHY_INTERFACE_H
 #define _PHY_INTERFACE_H
 
+#include <string.h>
+
 typedef enum {
 	PHY_INTERFACE_MODE_MII,
 	PHY_INTERFACE_MODE_GMII,