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/board/Marvell/db-88f6281-bp/db-88f6281-bp.c b/board/Marvell/db-88f6281-bp/db-88f6281-bp.c
index b68f2f3..729516d 100644
--- a/board/Marvell/db-88f6281-bp/db-88f6281-bp.c
+++ b/board/Marvell/db-88f6281-bp/db-88f6281-bp.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+
 
 #include <common.h>
+#include <net.h>
 #include <linux/io.h>
 #include <miiphy.h>
 #include <netdev.h>