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>

net/eth_legacy.c

@@ -8,6 +8,7 @@
 #include <common.h>
 #include <bootstage.h>
 #include <command.h>
+#include <dm.h>
 #include <env.h>
 #include <log.h>
 #include <net.h>