common: Move reset_phy() to net.h

This is a network function so let's move it into that header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/net.h b/include/net.h
index a8ee081..8a02c92 100644
--- a/include/net.h
+++ b/include/net.h
@@ -917,4 +917,12 @@
 {
 	return string_to_ip(env_get(var));
 }
+
+/**
+ * reset_phy() - Reset the Ethernet PHY
+ *
+ * This should be implemented by boards if CONFIG_RESET_PHY_R is enabled
+ */
+void reset_phy(void);
+
 #endif /* __NET_H__ */